arm32: filmgrain: Add NEON implementation of fgy and fguv for 16 bpc

Relative speedup over C code:
                                Cortex A7     A8     A9    A53    A72    A73
fguv_32x32xn_16bpc_420_csfl0_neon:   3.47   1.72   2.99   4.18   2.68   6.19
fguv_32x32xn_16bpc_420_csfl1_neon:   3.24   1.36   2.58   3.78   2.73   5.27
fguv_32x32xn_16bpc_422_csfl0_neon:   3.57   2.07   3.05   4.32   2.74   6.20
fguv_32x32xn_16bpc_422_csfl1_neon:   3.33   1.44   2.62   3.89   2.71   5.28
fguv_32x32xn_16bpc_444_csfl0_neon:   3.48   1.69   3.06   4.48   2.97   6.69
fguv_32x32xn_16bpc_444_csfl1_neon:   3.06   1.16   2.36   3.85   2.75   5.19
fgy_32x32xn_16bpc_neon:              2.89   1.05   2.29   3.49   2.49   3.15

Absolute numbers:
                                  Cortex A7       A8       A9      A53      A72      A73
fguv_32x32xn_16bpc_420_csfl0_neon:   6237.3  12701.0   6687.1   4525.8   3220.8   3195.4
fguv_32x32xn_16bpc_420_csfl1_neon:   5143.2  11684.8   5926.4   3857.2   2604.7   2556.5
fguv_32x32xn_16bpc_422_csfl0_neon:   6347.3  11005.2   6797.5   4582.4   3300.4   3250.5
fguv_32x32xn_16bpc_422_csfl1_neon:   5275.2  11594.8   5992.6   3931.1   2668.7   2607.3
fguv_32x32xn_16bpc_444_csfl0_neon:   5181.6  11310.0   5575.4   3629.7   2383.8   2530.0
fguv_32x32xn_16bpc_444_csfl1_neon:   4081.9  10958.8   4868.5   2962.9   1870.3   2034.2
fgy_32x32xn_16bpc_neon:             15439.1  43129.0  19406.6  11542.3   7463.9   7827.8

Corresponding numbers for arm64:
                                                            Cortex A53      A72      A73
fguv_32x32xn_16bpc_420_csfl0_neon:                              4019.2   3247.4   3259.6
fguv_32x32xn_16bpc_420_csfl1_neon:                              3460.1   2628.7   2640.8
fguv_32x32xn_16bpc_422_csfl0_neon:                              4034.4   3329.9   3287.5
fguv_32x32xn_16bpc_422_csfl1_neon:                              3468.3   2749.3   2686.6
fguv_32x32xn_16bpc_444_csfl0_neon:                              3117.7   2447.4   2539.8
fguv_32x32xn_16bpc_444_csfl1_neon:                              2641.2   1977.2   2132.8
fgy_32x32xn_16bpc_neon:                                         9873.5   7605.7   7656.2
38 jobs for master in 7 minutes and 4 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Style
passed style-check #669531
amd64 docker

00:00:07

passed x86inc-check #669532
amd64 docker

00:00:07

 
  Build
passed build-android-aarch64 #669547
amd64 docker

00:00:10

passed build-android-armv7 #669546
amd64 docker

00:00:12

passed build-debian #669533
amd64 avx2 docker

00:00:27

passed build-debian-aarch64 #669548
aarch64 docker

00:00:40

passed build-debian-aarch64-clang-5 #669549
aarch64 docker

00:00:12

passed build-debian-armv7 #669552
armv7 docker

00:02:03

passed build-debian-armv7-clang-5 #669553
armv7 docker

00:00:29

passed build-debian-bitdepth-16 #669540
amd64 docker

00:00:13

passed build-debian-bitdepth-8 #669539
amd64 docker

00:00:18

passed build-debian-examples #669537
amd64 docker

00:00:17

passed build-debian-illegal-instructions #669535
amd64 avx2 docker

00:01:58

passed build-debian-no-tools #669538
amd64 docker

00:00:18

passed build-debian-ppc64le #669555
ppc64le docker

00:02:02

passed build-debian-static #669534
amd64 docker

00:00:31

passed build-debian-werror #669551
aarch64 docker

00:00:16

passed build-debian32 #669536
amd64 docker

00:00:28

passed build-macos #669550
catalina amd64

00:01:10

passed build-ubuntu-snap #669554
amd64 docker

00:00:25

passed build-win-arm32 #669544
amd64 docker

00:00:12

passed build-win-arm64 #669545
amd64 docker

00:00:13

passed build-win32 #669541
amd64 docker

00:00:35

passed build-win32-unaligned-stack #669542
amd64 docker

00:00:26

passed build-win64 #669543
amd64 docker

00:00:51

 
  Test
passed test-debian #669556
amd64 docker

00:01:19

95.6871%
passed test-debian-aarch64 #669589
aarch64 docker

00:00:27

passed test-debian-armv7-clang-5 #669567
armv7 docker

00:01:27

passed test-debian-asan #669560
amd64 docker

00:02:40

passed test-debian-asm #669557
avx2 amd64 docker

00:00:54

passed test-debian-msan #669561
amd64 docker

00:01:01

passed test-debian-ppc64le #669566
ppc64le docker

00:02:59

passed test-debian-tsan #669563
amd64 docker

00:03:11

passed test-debian-ubsan #669562
amd64 docker

00:01:18

passed test-debian-unaligned-stack #669559
amd64 avx2 docker

00:00:55

passed test-debian32-asm #669558
avx2 amd64 docker

00:00:58

passed test-win64 #669564
amd64 avx2 docker

00:04:31

canceled test-debian-aarch64 #669565
aarch64 docker

00:14:22