msm: kgsl: Hook preemption sysfs nodes to hwscheduling

With hwscheduling, we need to communicate the preemption parameters
to GMU. Also, we need to use GET_VALUE hfi packet to get the
number of preemptions since last SLUMBER exit.

Change-Id: I2ab342817a3cea4e1d1797369aa272895730357b
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>