Added CFL_SUB8X8_VAL_MI_SIZE and CFL_SUB8X8_VAL_MI_SQUARE to replace the
magic numbers previously used. Also, CFL_SUB8X8_VAL_MI_SIZE goes from 2
to 4 to support the upcoming EXT_PARTITION_TYPE experiment.

Change-Id: I5c812af3366f80345a749451415660024e41ea3c