msm: mdss: update the programmable line value during VRR

Update the programmable fetch start line register during variable
refresh rate (VRR) operations. This is needed since the vertical
front porch value changes when there is a change in fps. Also, do
not perform fetch start configuration during boot up when
continuous splash screen is enabled. The feature will be enabled in
LK. This is needed for proper VRR operations until first suspend
resume.

Change-Id: I5c82bc520da53db958ad0fad4217f00d92a25cae
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>