msm: kgsl: Support adding VA padding for global allocations

Most of the global buffers are allocated sequentially in the GPU virtual
memory space. Some buffers might want to have a bit of breathing room to
try to detect buffer overwrites. Allow specific buffers to allocate some
additional virtual address padding. To start, add a 4K gap between
ringbuffers and a 16K space after the preemption records.

Change-Id: Ic0dedbadb7bdd39a87228e222990700f3727f51e
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>