msm: kgsl: Add property to determine GPU bitness

Add the property to determine GPU bitness which
is used by the clients via KGSL ioctl.

Certain clients of KGSL such as Open-CL driver
need to know explicitly about the GPU mode.

Change-Id: I77523d7816edb9776014aaf3aa85321af0d20aaf
Signed-off-by: Sunil Khatri <sunilkh@codeaurora.org>