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

Update 1.8G ab and ib bandwidth vote during continuous
splash usecase to avoid underrun on video mode and
long frame transfer time on command mode.

Change-Id: I01fadbd857e337bea648cbc0e53dfc4460ec059d
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>