arm64: filmgrain: Add NEON implementation of the generate_grain_uv functions

The existing functions/macros for generate_grain_y are templated
for adding in the a final coefficient from the y buffer, while
trying to keep the binary size down.

Relative speedup over C code:
                            Cortex A53    A72    A73   Apple M1
gen_grain_uv_ar0_8bpc_420_neon:   4.62   4.55   5.27   9.08
gen_grain_uv_ar0_8bpc_422_neon:   4.81   4.90   5.33   7.25
gen_grain_uv_ar0_8bpc_444_neon:   5.05   5.17   5.69   7.04
gen_grain_uv_ar1_8bpc_420_neon:   3.61   3.09   3.68   3.92
gen_grain_uv_ar1_8bpc_422_neon:   3.71   3.22   3.64   3.46
gen_grain_uv_ar1_8bpc_444_neon:   3.59   3.40   3.67   3.11
gen_grain_uv_ar2_8bpc_420_neon:   4.77   3.85   4.81   4.55
gen_grain_uv_ar2_8bpc_422_neon:   4.88   3.96   4.85   4.15
gen_grain_uv_ar2_8bpc_444_neon:   5.18   4.65   5.18   3.83
gen_grain_uv_ar3_8bpc_420_neon:   6.14   5.25   6.14   5.64
gen_grain_uv_ar3_8bpc_422_neon:   6.27   5.27   6.28   5.42
gen_grain_uv_ar3_8bpc_444_neon:   6.84   6.40   6.79   5.18
38 jobs for arm64-gen-grain-uv in 6 minutes and 31 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Style
passed #630689
amd64 docker
style-check

00:00:07

passed #630690
amd64 docker
x86inc-check

00:00:07

 
  Build
passed #630705
amd64 docker
build-android-aarch64

00:00:10

passed #630704
amd64 docker
build-android-armv7

00:00:11

passed #630691
amd64 avx2 docker
build-debian

00:00:26

passed #630706
aarch64 docker
build-debian-aarch64

00:00:16

passed #630707
aarch64 docker
build-debian-aarch64-clang-5

00:00:14

passed #630710
armv7 docker
build-debian-armv7

00:01:40

passed #630711
armv7 docker
build-debian-armv7-clang-5

00:00:28

passed #630698
amd64 docker
build-debian-bitdepth-16

00:00:10

passed #630697
amd64 docker
build-debian-bitdepth-8

00:00:20

passed #630695
amd64 docker
build-debian-examples

00:00:16

passed #630693
amd64 avx2 docker
build-debian-illegal-instructions

00:01:33

passed #630696
amd64 docker
build-debian-no-tools

00:00:21

passed #630713
ppc64le docker
build-debian-ppc64le

00:01:08

passed #630692
amd64 docker
build-debian-static

00:00:23

passed #630709
aarch64 docker
build-debian-werror

00:00:17

passed #630694
amd64 docker
build-debian32

00:00:27

passed #630708
catalina amd64
build-macos

00:01:01

passed #630714
amd64 docker
build-pages

00:00:09

passed #630712
amd64 docker
build-ubuntu-snap

00:00:24

passed #630702
amd64 docker
build-win-arm32

00:00:10

passed #630703
amd64 docker
build-win-arm64

00:00:19

passed #630699
amd64 docker
build-win32

00:00:35

passed #630700
amd64 docker
build-win32-unaligned-stack

00:00:23

passed #630701
amd64 docker
build-win64

00:00:49

 
  Test
passed #630715
amd64 docker
test-debian

00:01:12

95.791%
passed #630724
aarch64 docker
test-debian-aarch64

00:00:28

passed #630726
armv7 docker
test-debian-armv7-clang-5

00:01:28

passed #630719
amd64 docker
test-debian-asan

00:02:30

passed #630716
avx2 amd64 docker
test-debian-asm

00:00:51

passed #630720
amd64 docker
test-debian-msan

00:01:26

passed #630725
ppc64le docker
test-debian-ppc64le

00:02:53

passed #630722
amd64 docker
test-debian-tsan

00:02:35

passed #630721
amd64 docker
test-debian-ubsan

00:01:37

passed #630718
amd64 avx2 docker
test-debian-unaligned-stack

00:01:02

passed #630717
avx2 amd64 docker
test-debian32-asm

00:00:52

passed #630723
amd64 avx2 docker
test-win64

00:03:33