drm/msm/sde: update 1.8G BW vote during cont-splash

During power enable for the first time, data bus vote is
0 ab and 400 Mbp ib. In few scenarios this reduction in vote
during continuous splash for few ms is causing underrun.
Update 1.8G ab and ib bandwidth vote at first power enable
to avoid underrun on video mode in continuous splash usecase.

Change-Id: I2a72b0603c1515a4bf530c8adcf421845531d497
Signed-off-by: Raviteja Tamatam <travitej@codeaurora.org>