[x265] arm64 neon asm optimizations

[Damiano Galassi]

Hi, Apple contributed to the HandBrake project a x265 patch
with a bunch of neon asm to improve x265 performance on Apple’s upcoming ARM Macs,
but I don’t have the expertise or the time to review these changes, all I can do is send this patch to you.
The code contributed by Apple is under MIT license and without any "copyright assertion on it”.

The neon asm speeds up is almost 2x, so I hope someone will try to integrate it.
The additions are viewable on https://github.com/HandBrake/HandBrake/commit/67a490a171764eafe8eb8afb72fa1dff763a3275

Regards,
Damiano Galassi