drm/amd/display: Update MBLK calculation for SubVP

[Description]
Update MBLK calculation according to hardware doc.  For DCC case we were
not allocation enough MALL due to an inaccurate MBLK calculation.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Pavle Kotarac <Pavle.Kotarac@amd.com>
Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>