msm: kgsl: Expose HFI get and set value over sysfs

For LM characterization, a user must be able to get and
set register values over HFI, using adb. Expose sysfs nodes for
address and value that can be used for this purpose.

Change-Id: I54678d9caf8c0a60623ecd8568dd787132feb92d
Signed-off-by: Kyle Piefer <kpiefer@codeaurora.org>
Signed-off-by: Mohammed Mirza Mandayappurath Manzoor <mmandaya@codeaurora.org>