msm: kgsl: Remove the preemption oob

This oob is needed in a corner case of preemption
state machine, where we need to read the wptr to
see if it needs to be updated. But in cases where it
doesn't need to be updated, we have forcibly brought
gpu out of ifpc for nothing. Instead, use a flag to
figure the corner case, and then use a fenced write
only when wptr needs update.

Change-Id: I1b111d187c982fd2102c1e1c4d2b8f93bd7d18eb
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>