Reclasify optimized ssim calculations as SSE2.

Calculations were incorrectly classified as either
SSE3 or SSSE3.  Only using SSE2 instructions.
Cleanup function names and make non-RTCD code work
as well.

Change-Id: I29f5c2ead342b2086a468029c15e2c1d948b5d97
6 files changed