msm: kgsl: Enable the perfcounters with a protected mode packet

The perfcounter select registers may be write-protected from GPU
writes. Set the protected mode flag when enabling them through the
GPU path.

Change-Id: I255cc4e95ef36e5cddf559dc32add142ceaddc75
Signed-off-by: Lynus Vaz <lvaz@codeaurora.org>