aarch64: add DAV1D_ARM_CPU_FLAG_DOTP

Runtime detection on Linux using HWCAP_CPUID for user space access to
the CPU feature registers. See
https://www.kernel.org/doc/html/latest/arm64/cpu-feature-registers.html

Runtime detection on MacOS using sysctlbyname("hw.cpufamily") and matching
known ARMv8.4-A CPUs. MacOS unfortunately doesn't expose a flag for this
feature.
35 jobs for arm64_cpuid in 6 minutes and 21 seconds (queued for 3 seconds)
latest
Status Job ID Name Coverage
  Style
passed #545960
amd64 docker
style-check

00:00:07

passed #545961
amd64 docker
x86inc-check

00:00:06

 
  Build
passed #545973
amd64 docker
build-android-aarch64

00:00:12

passed #545972
amd64 docker
build-android-armv7

00:00:10

passed #545962
amd64 avx2 docker
build-debian

00:00:24

passed #545974
aarch64 docker
build-debian-aarch64

00:00:16

passed #545975
aarch64 docker
build-debian-aarch64-clang-5

00:00:21

passed #545978
armv7 docker
build-debian-armv7

00:00:43

passed #545979
armv7 docker
build-debian-armv7-clang-5

00:00:35

passed #545965
amd64 docker
build-debian-examples

00:00:23

passed #545966
amd64 docker
build-debian-no-tools

00:00:18

passed #545981
ppc64le docker
build-debian-ppc64le

00:02:22

passed #545963
amd64 docker
build-debian-static

00:00:27

passed #545977
aarch64 docker
build-debian-werror

00:00:08

passed #545964
amd64 docker
build-debian32

00:00:24

passed #545976
catalina amd64
build-macos

00:00:43

passed #545982
amd64 docker
build-pages

00:00:09

passed #545980
amd64 docker
build-ubuntu-snap

00:00:19

passed #545970
amd64 docker
build-win-arm32

00:00:11

passed #545971
amd64 docker
build-win-arm64

00:00:14

passed #545967
amd64 docker
build-win32

00:00:38

passed #545968
amd64 docker
build-win32-unaligned-stack

00:00:26

passed #545969
amd64 docker
build-win64

00:00:40

 
  Test
passed #545983
amd64 docker
test-debian

00:01:19

95.8258%
passed #545992
aarch64 docker
test-debian-aarch64

00:00:26

passed #545994
armv7 docker
test-debian-armv7-clang-5

00:01:09

passed #545987
amd64 docker
test-debian-asan

00:02:01

passed #545984
avx2 amd64 docker
test-debian-asm

00:01:03

passed #545988
amd64 docker
test-debian-msan

00:01:04

passed #545993
ppc64le docker
test-debian-ppc64le

00:03:47

passed #545990
amd64 docker
test-debian-tsan

00:04:17

passed #545989
amd64 docker
test-debian-ubsan

00:01:37

passed #545986
amd64 avx2 docker
test-debian-unaligned-stack

00:00:49

passed #545985
avx2 amd64 docker
test-debian32-asm

00:01:06

passed #545991
amd64 avx2 docker
test-win64

00:01:42