i965: Add mask_control_ex field and handle it in compaction.

i965: Add mask_control_ex field and handle it in compaction.

Documentation is sparse, but it appears to have existed on G45 and ILK
as a second bit extension of the mask_control field. Setting the pair of
bits to 0b11 enables "NoCMask".

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>