msm_fb: display: Increase MDP IOMMU buffer mapping size

Double the MDP IOMMU buffer mapping size to allow overfetching
by hardware for boundary conditions and avoid system crashes
due to page faults.

CRs-Fixed: 378108
CRs-Fixed: 364478
Signed-off-by: Ravishangar Kalyanam <rkalya@codeaurora.org>
Change-Id: Ib19af6b06ab06455acaffcca33830e0487bb0836
(cherry picked from commit 1ed0dae869f6384d23322b78691852d70c573174)