msm: mdss: fix black screen issue on 8909MTP

Black screen is seen on command mode panel because clock
MDP are getting turned off during probe.
Keep the clock on for video mode panel when splash is enabled.

Change-Id: I6cd9831f068704a61f8c0667cdd72e1798c68349
Signed-off-by: Sravanthi Kollukuduru <skolluku@codeaurora.org>