Usage of CPU by round_shift_array goes from 2.01% to 1.04%.
Overall encoding is slightly faster (~0.05%).

This means some of the intermediate array have to be aligned.
Also, these functions were moved to common header/source files.

BUG=aomedia:1106

Change-Id: I492c9b1f2e7339c6cb83cfe68a61218642654d1b