disp: msm: sde: correct line time to include DSC

Current computation of line time does not include compression ratio from
DSC. This change computes compression ratio during any mode change
and stores it in sde_crtc.

Change-Id: Ib1e045dce17fcf006447d4562b402cc3f214ed8c
Signed-off-by: Samantha Tran <samtran@codeaurora.org>