msm: mdss: unblank panel when entering doze mode for video mode panels

For video mode panels, MDSS hardware needs to be on as long as the
panel is on. When doze mode is requested for a video mode panel,
no special optimizations can be done in the display driver to
configure the hardware in a low power state. As such, when doze mode is
requested for video mode panels, simply unblank the panel if it is not
already on.

Change-Id: I0f279d78b9b5c8eebb2bf654df628acafa408f23
Signed-off-by: Aravind Venkateswaran <aravindh@codeaurora.org>