msm: kgsl: Improve logs for pagefaults on global buffers

Log the nearby allocations for pagefaults on global buffers.
Print the names of the allocations that fall around the
faulting address on a global buffer. Also add a new debugfs
file to list all the global pagetable entries. Useful for
debugging pagefaults and other issues with "global" objects.

CRs-Fixed: 985631
Change-Id: Ifbbdc69044fc64d7ea02509bf8113ed94eeece1e
Signed-off-by: Sushmita Susheelendra <ssusheel@codeaurora.org>