msm: kgsl: Don't dump GPMU registers on non GPMU devices

In Snapshot path, GPMU register offsets are being dumped on all A5xx
devices. But some targets on A5xx does not have GPMU. So accessing GPMU
registers would cause device fault.
Allow the GPMU register access only on targets with GPMU.

Change-Id: I2885dbdaf1cc95f960dcfacad52d6ded1dc9ac1d
Signed-off-by: Venkateswara Rao Tadikonda <vtadik@codeaurora.org>