General cleanups.

Removing unused constants, macros, and function declarations. Using
ROUND_POWER_OF_TWO macro, vp9_zero, vp9_copy where possible. Moving
#include from *.h to *.c. Merging for loops for motion vectors.

Change-Id: Ic3bf841764a2bb177128bb3a6d7aa8f68229cd13
18 files changed