msm: mdss: reserve memory for splash screen on 8x10

Earlier, display driver was allocating the memory for
splash screen feature.   The splash image was copied
to the allocated memory during LK to kernel transition.
Now, instead of allocating and copying, display driver
reserves the splash screen memory until the first display
update.

Change-Id: Ie5f0aa17dceaa826eddab1e5b4b705a3ea287a1a
Signed-off-by: Xiaoming Zhou <zhoux@codeaurora.org>