x86: SSE and AVX implementations of plane_copy

Also remove the MMX2 implementation and fix src overread for height == 1.
Improve HRD conformance
New AQ mode: auto-variance AQ with bias to dark scenes

Also known as --aq-mode 3 or auto-variance AQ modification.
x86: Update intel compiler cpu dispatcher override for new versions of ICC/ICL
NV21 input support

Eliminates an extra copy when encoding Android camera preview images.

Checkasm test by Janne Grunau.
ARM assembly with improvements from Janne Grunau.
x86: SSSE3 and AVX2 implementations of plane_copy_swap

For NV21 input.