try plain-old code for sk_memset16/32 now that NEON is compile-time

Most of these implementations now just say "always inline".
Let's see if we can get away with the simplicity of doing that all the time.

These inlined implementations can autovectorize easily.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1639863002
CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Review URL: https://codereview.chromium.org/1639863002
5 files changed