msm: kgsl: Refactor GPU addressing

32 bit addresses can take us only so far. The current state of the driver
works great for 32 bit address but not so much for 64 bit addresses. Put
a generic memory mapping code into place that will allow for 32 bit or 64
bit addressing schemes.

Change-Id: Ic0dedbadb8d0e44a0914f99c223b398fb9fde153
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>