Fixes to disable MFQE when there is motion.

This patch includes:
1. fixes to disable block based termporal mixing when motion
is detected (because this version of mfqe only handles zero motion).
2. The criterion used for determining whether to mix or
not are changed to use squared differences rather than
absolute differences.
3. Additional checks on color mismatch and excessive block
flatness added. If the block as decoded has very low activity
it is unlikely to yield benefits for mixing.

Change-Id: I07331e5ab5ba64844c56e84b1a4b7de823eac6cb