arm32: mc: Add NEON implementation of emu_edge for 16 bpc

Checkasm benchmarks:    Cortex  A7       A8      A53      A72     A73
emu_edge_w4_16bpc_neon:      375.0    312.6    268.3    159.3   170.0
emu_edge_w8_16bpc_neon:      619.3    425.5    435.5    249.5   291.1
emu_edge_w16_16bpc_neon:     719.1    568.3    506.9    324.2   314.4
emu_edge_w32_16bpc_neon:    2112.2   1677.7   1396.2   1050.5  1009.6
emu_edge_w64_16bpc_neon:    5046.8   4322.5   3693.7   3953.8  2682.8
emu_edge_w128_16bpc_neon:  16311.1  14341.3  12877.8  26183.5  8924.9

Corresponding numbers for arm64, for comparison:
                                         Cortex A53      A72      A73
emu_edge_w4_16bpc_neon:                       302.5    174.9    159.2
emu_edge_w8_16bpc_neon:                       344.6    292.3    273.2
emu_edge_w16_16bpc_neon:                      601.0    461.2    316.8
emu_edge_w32_16bpc_neon:                      974.2   1274.7    960.5
emu_edge_w64_16bpc_neon:                     2853.1   3527.6   2633.5
emu_edge_w128_16bpc_neon:                   14633.5  26776.6   7236.0
34 jobs for arm32-mc16 in 8 minutes and 17 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Style
passed #505796
amd64 docker
style-check

00:00:17

passed #505797
amd64 docker
x86inc-check

00:00:17

 
  Build
passed #505808
amd64 docker
build-android-aarch64

00:00:18

passed #505807
amd64 docker
build-android-armv7

00:00:24

passed #505798
amd64 avx2 docker
build-debian

00:00:25

passed #505809
aarch64 docker
build-debian-aarch64

00:00:25

passed #505810
aarch64 docker
build-debian-aarch64-clang-5

00:00:24

passed #505813
armv7 docker
build-debian-armv7

00:00:41

passed #505814
armv7 docker
build-debian-armv7-clang-5

00:00:35

passed #505801
amd64 docker
build-debian-examples

00:00:19

passed #505816
ppc64le docker
build-debian-ppc64le

00:01:13

passed #505799
amd64 docker
build-debian-static

00:00:24

passed #505812
aarch64 docker
build-debian-werror

00:00:20

passed #505800
amd64 docker
build-debian32

00:00:25

passed #505811
macos
build-macos

00:00:59

passed #505817
amd64 docker
build-pages

00:00:14

passed #505815
amd64 docker
build-ubuntu-snap

00:00:27

passed #505805
amd64 docker
build-win-arm32

00:00:18

passed #505806
amd64 docker
build-win-arm64

00:00:23

passed #505802
amd64 docker
build-win32

00:00:40

passed #505803
amd64 docker
build-win32-unaligned-stack

00:00:36

passed #505804
amd64 docker
build-win64

00:00:57

 
  Test
passed #505818
amd64 docker
test-debian

00:01:15

97.8919%
passed #505827
aarch64 docker
test-debian-aarch64

00:00:38

passed #505829
armv7 docker
test-debian-armv7-clang-5

00:00:52

passed #505823
amd64 docker
test-debian-asan

00:02:04

passed #505819
avx2 amd64 docker
test-debian-asm

00:01:13

passed #505824
amd64 docker
test-debian-msan

00:00:40

passed #505821
amd64 docker
test-debian-mt

00:00:42

passed #505828
ppc64le docker
test-debian-ppc64le

00:01:50

passed #505825
amd64 docker
test-debian-ubsan

00:01:24

passed #505822
amd64 avx2 docker
test-debian-unaligned-stack

00:00:52

passed #505820
avx2 amd64 docker
test-debian32-asm

00:00:49

passed #505826
amd64 avx2 docker
test-win64

00:01:05