msm: kgsl: Skip gpu registers dumping when gx is off

GPU registers can't be accessed if the gx headswitch is off.
During the gx off case access to GPU gx blocks will show data
as 0x5c00bd00. Hence skip dumping GPU registers during gx off.

Change-Id: I2fec5280c3867054620427327820e0302a29255b
Signed-off-by: Sravankumar bijili <csbijil@codeaurora.org>