msm: kgsl: Improve GPU soft fault detection

Following changes been made to improve soft fault detection,
which will fix un clocked register access in dispatcher_do_fault()
and incorrect declaration of GPU soft fault.
i) Stop fault timer before entering to NAP state
ii) Don’t start fault timer if the dispatcher inflight count is zero
iii) Add ringbuffer empty check in _isidle()
iv)  Add device state check in dispatcher_do_fault()

CRs-Fixed: 2012731
Change-Id: I5ce498029f389eeeb428b4ac7fb07afd84d5764c
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>