Ensure HBD/LBD joint compound to generate matching result
Ensure HBD/LBD joint compound to generate matching result

This patch followed the previous HBD quantizer fix, and continued
to fix the bitstream mismatch issue between CONFIG_LOWBITDEPTH=0
and CONFIG_LOWBITDEPTH=1. The bug was that a joint compound SIMD
function didn't match the c version. A unit test should be added
after fixing this function.

STATS_CHANGE
BUG=aomedia:1613

Change-Id: I18a88257c09f09217eb02f79caca918206caa432

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom