x86: Minor mbtree_propagate_cost improvements

Reduce the number of registers used from 7 to 6.
Reduce the number of vector registers used by the AVX2 implementation from 8 to 7.
Multiply fps_factor by 1/256 once per frame instead of once per macroblock row.
Use mova instead of movu for dst since it's guaranteed to be aligned.
Some cosmetics.
support frame-packing values in Matroska
x86inc: fix FMA_INSTR to work when arguments 1 and 4 are the same

This involves a 5th argument to use as a temp, so the macro is moved to
x86util instead.
Fix build with Android NDK

Android NDK does not expose sched_getaffinity.