drm/msm/sde: increase bus votes only during cont-splash

During no cont-splash use case the data bus votes were
increased to 1.8 GBps. Made changes to increase only
during the use case.

Change-Id: I882bd67228fd7393a4c025706a32f60da52abd1d
Signed-off-by: Raviteja Tamatam <travitej@codeaurora.org>