msm: kgsl: Check before resetting timestamps of 2D core to 0 on startup

The timestamp of 2D core should not be set to 0 on startup if the
device has previously been started and is waking up from a suspend call.
This can cause processes to wait indefinitely for the 2D core if
they received a timestamp before the device went into suspend

Change-Id: Ida5dbdcb89ea7e0cf86110ecc2bd7d568123c364
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>