msm: kgsl: Add options to enable/disable preemption

Options to enable/disable preemption are required for debugging
if preemption is the cause of stability or performance issues.

Add sysfs option to enable/disable preemption.
echo 0 > /sys/class/kgsl/kgsl-3d0/preemption to disable preemption.
echo 1 > /sys/class/kgsl/kgsl-3d0/preemption to enable preemption.
cat /sys/class/kgsl/kgsl-3d0/preemption to see the current state
of preemption.

Add a module parameter to disable preemption at boot. Module parameter
allows preemption to be disabled from the kernel command line for debugging
purposes.

Change-Id: Ic831e2c109e4114bc6f27d66dc0e72bfacd7ab32
Signed-off-by: Tarun Karra <tkarra@codeaurora.org>