msm: mdss: Enable true continuous splash in mdp3

Black screen was seen during lk to kernel transition,
because iommu was attached after stopping the DMA transfer.
Now buffer is mapped in iommu page table with same
virtual and physical address. This will allow dynamic attach
of iommu and enable true continuous splash.

Change-Id: I4cd117cb46dcc2ef1fd31ba935e3da0e6f2e940e
Signed-off-by: Ramakant Singh <ramaka@codeaurora.org>