hbd lpf sse2 perf and code quality improvement
hbd lpf sse2 perf and code quality improvement

aom_highbd_lpf_horizontal_14_sse2 -1.15x perf
due to full sse2 register width usage for some ops
highbd_hev_filter_mask_x_sse2 added for code quality
if blocks in _4,_6,_8 and _14 eliminated

Change-Id: Ie28a70798833c95fb21cac238ffdebfcead5f0a7

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