msm: kgsl: Use a different register to convey log info to GMU

The GENERAL_6 scratch register is already used for some other
purpose. So, use GMU_PWR_COL_CP_MSG to convey the master log
base address and size to the GMU.

Change-Id: I9df720dffb594d745a8fb1506fc64000e2abe5d1
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>