x86 asm for high-bit-depth pixel metrics

x86 asm for high-bit-depth pixel metrics
Overall speed change from these 6 asm patches: ~4.4x.
But there's still tons more asm to do -- patches welcome!

Breakdown from this patch:
~13x faster SAD than C.
~11.5x faster SATD than C (only MMX done).
~18.5x faster SA8D than C.
~19.2x faster hadamard_ac than C.
~8.3x faster SSD than C.
~12.4x faster VAR than C.
~3-4.2x faster intra SAD than C.
~7.9x faster intra SATD than C.