msm: kgsl: GPMU interrupt handling code

This patch updates KGSL interrupt code to handle GPMU voltage
droop and watchdog bite. Bit 28 of the RBBM interrupt status
register indicates a voltage droop issue, and driver needs to
print out an error message. Bit 29 of this status register
together with Bit 31 of the GPMU interrupt information register
indicate a GPMU watchdog timeout, which requires a reset of GPMU.

Change-Id: I72a5ecf74d694979ce1b90cba58a255710caa8a0
Signed-off-by: Yizheng Zhou <yizhengz@codeaurora.org>