Add high bit-depth macro definitions:
highbd_jnt_sad
highbd_8(10/12)_jnt_sub_pixel_avg.

Add SIMD functions:
aom_highbd_jnt_comp_avg_pred_sse2
aom_highbd_jnt_comp_avg_upsampled_pred_sse2

This patch also solves the seg fault caused by low bit-depth and
high bit-depth paths

BUG=aomedia:967
BUG=aomedia:944

Change-Id: Iea69f114e81ca226a30d84a540ad846f1b94b8d6