msm: kgsl: For soft fault detect only check rbbm_status

When deciding whether device has faulted or not using soft fault
detect only check the status of rbbm_status register and skip
checking interrupt status. Also, if device is detected to be
idle based on rbbm_status then there is no need to check the
timestamps because if another thread is about to submit
something to hardware then the timestamps will not match.

Change-Id: I3c14ec6ef18040a5b8ace250c4deaa4e693544bb
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>