msm: kgsl: Fix the address translation ranges for GPU IOMMU

Set the address translation to happen via ttbr0 for GPU IOMMU till
address 0x80000000 instead of 0x40000000. Also, adjust the size of
virtual pool so that it does not allocate an address greater
than 0x80000000.

CRs-fixed: 401364
Change-Id: I268dda47e82e80a7ee0a72a835c7777be8b6f7f5
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>