[CFL] Add support for CHROMA_SUB8X8

When chroma_sub8x8 is enable the custom DC_PRED implemented in CfL uses
chroma_up_available and chroma_left_available instead of up_available
and left_available.

It was mentioned in 3da18d60a53b55758093d1db864114168dd0368c that
this fixes a rare enc/dec mismatch issue.

Change-Id: Ie8920e956962846db15e24bcf7e7eaa13ccb8c12
1 file changed