drm/msm/sde: increase Bus BW ib/ab vote during cont-splash

Increase the Bus BW ib/ab vote during sde driver probe
to 3G. This is to support 4k@70 fps usecases.

Change-Id: Ifc61ded2a80280931996d4f1c4114a503a820d36
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>