msm: mdss: support transition from suspend to doze mode

If a transition from full suspend to doze mode is requested, first
unblank the panel and then enter the doze mode. This is necessary
to ensure that all necessary panel supplies are turned on and the
panel is brought out of reset first.

Change-Id: I5757f01ec9843a332fd2d1034c068ff993f466bd
Signed-off-by: Aravind Venkateswaran <aravindh@codeaurora.org>