drm/msm/sde: CCN Cleanup for sde_crtc

Add changes in the sde crtc to reduce
CCN (Cyclomatic Complexity Number) to less than thirty.

Change-Id: I91e10b9eede69475c8031c591aa8026814874f3a
Signed-off-by: Nilaan Gunabalachandran <ngunabal@codeaurora.org>