vp9-skinmap. Some adjustments for model=1.

-use larger threshold on y (as in vp8).
-add distance threshold for each cluster
-use larger skin distance threshold for first cluster
-add some early exist checks.

Keep default setting to model=0.

Change-Id: I1044b99ade4bb1f215a860a019a4d84cee2f7715
1 file changed