msm: kgsl: Update ringbuffer timer when preemption completes

Ringbuffer timer should always be reset whenever we finish
preempting to that ringbuffer. Currently, there is a case where
wptr in the hardware and the kgsl are identical and thus
the timer isn't reset. Reset the timer regardless if they are
identical or not.
There is one special case when we shouldn't reset the timer.
This happens when we try to figure out next ringbuffer to preempt
but the next ringbuffer is the same one as current. In that case,
if nothing new got submitted to this ringbuffer, then don't reset
the timer.

Change-Id: I6b5aea46f1769021b39ba6e135bef780719a92e7
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>