mdss: mdss_fb: remove mmio access through mmap

Disable access to mm io and add
appropriate range checks to ensure valid accesses
through framebuffer mmap. This prevents illegal
access into memory.

Change-Id: Ic6e47ec726d330d48ce9a7a708418492a553543b
CRs-Fixed: 474706
Signed-off-by: Manoj Rao <manojraj@codeaurora.org>