Add CoeffHalfDequant test
Add CoeffHalfDequant test

Force the coeff to be half the value of the dequant.  This exposes a
mismatch found in av1_quantize_fp_sse2().

BUG=aomedia:1668

Change-Id: I0323ce91799b53b2ec17ba0b8c7c737e1c709f5f

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