msm: kgsl: Store power_interval_timeout in msec

Update to store power_interval_timeout in msec instead of jiffies,
to make it consistent across the board irrespective of the HZ value.

Change-Id: I157da71210268b5b436670452a4bd4ac6abbdcc7
Signed-off-by: Rohan Sethi <rohsethi@codeaurora.org>