simd.h: More support for ARM NEON (#2614)
simd.h: More support for ARM NEON (#2614)

Was browsing some NEON docs and took the opportunity to fill in
implementations of a few more simd methods.

I don't have a way to directly test this myself, but hopefully
simd_test.cpp has enough unit tests to uncover if I've used the wrong
intrinsics for any of this.

I'm hoping that soon GitHub will add a way to run CI jobs on ARM CPUs
for Mac, if nothing else, so we'll have a way to verify this
architecture.

Signed-off-by: Larry Gritz <f0a1ce6f80112d72f7276457fd261d671b827567@larrygritz.com>
lgritz/oiio,lgritz/oiio,OpenImageIO/oiio,OpenImageIO/oiio,OpenImageIO/oiio,lgritz/oiio,OpenImageIO/oiio,lgritz/oiio