arm64: Add NEON implementation of fgy_32x32xn

Relative speedup over C code:

                   Cortex A53    A72    A73   Apple M1
fgy_32x32xn_8bpc_neon:   4.48   2.84   3.73       5.64
38 jobs for arm64-fgy in 9 minutes and 49 seconds (queued for 1 minute and 11 seconds)
Status Job ID Name Coverage
  Style
passed #595096
amd64 docker
style-check

00:00:11

passed #595097
amd64 docker
x86inc-check

00:00:09

 
  Build
passed #595112
amd64 docker
build-android-aarch64

00:00:10

passed #595111
amd64 docker
build-android-armv7

00:00:10

passed #595098
amd64 avx2 docker
build-debian

00:00:24

passed #595113
aarch64 docker
build-debian-aarch64

00:00:16

passed #595114
aarch64 docker
build-debian-aarch64-clang-5

00:00:14

passed #595117
armv7 docker
build-debian-armv7

00:01:54

passed #595118
armv7 docker
build-debian-armv7-clang-5

00:01:24

passed #595105
amd64 docker
build-debian-bitdepth-16

00:00:12

passed #595104
amd64 docker
build-debian-bitdepth-8

00:00:19

passed #595102
amd64 docker
build-debian-examples

00:00:12

passed #595100
amd64 avx2 docker
build-debian-illegal-instructions

00:01:36

passed #595103
amd64 docker
build-debian-no-tools

00:00:14

passed #595120
ppc64le docker
build-debian-ppc64le

00:03:20

passed #595099
amd64 docker
build-debian-static

00:00:25

passed #595116
aarch64 docker
build-debian-werror

00:00:10

passed #595101
amd64 docker
build-debian32

00:00:18

passed #595115
catalina amd64
build-macos

00:00:49

passed #595121
amd64 docker
build-pages

00:00:08

passed #595119
amd64 docker
build-ubuntu-snap

00:00:19

passed #595109
amd64 docker
build-win-arm32

00:00:10

passed #595110
amd64 docker
build-win-arm64

00:00:12

passed #595106
amd64 docker
build-win32

00:00:35

passed #595107
amd64 docker
build-win32-unaligned-stack

00:00:30

passed #595108
amd64 docker
build-win64

00:00:38

 
  Test
passed #595122
amd64 docker
test-debian

00:01:18

95.8623%
passed #595131
aarch64 docker
test-debian-aarch64

00:00:27

passed #595133
armv7 docker
test-debian-armv7-clang-5

00:03:30

passed #595126
amd64 docker
test-debian-asan

00:02:40

passed #595123
avx2 amd64 docker
test-debian-asm

00:00:14

passed #595127
amd64 docker
test-debian-msan

00:01:18

passed #595132
ppc64le docker
test-debian-ppc64le

00:05:14

passed #595129
amd64 docker
test-debian-tsan

00:02:32

passed #595128
amd64 docker
test-debian-ubsan

00:01:30

passed #595125
amd64 avx2 docker
test-debian-unaligned-stack

00:00:47

passed #595124
avx2 amd64 docker
test-debian32-asm

00:00:14

passed #595130
amd64 avx2 docker
test-win64

00:03:31