msm: kgsl: Remove srcu notifier support

SRCU notifier calls were used to notify the adreno_tz governor
about a powerstat update. Since we have now moved to update_devfreq()
API, we can safely remove SRCU notifier support from the driver.

Change-Id: I791c1abfb00715a220c12e0b02b9740ec074e4aa
Signed-off-by: Akhil P Oommen <akhilpo@codeaurora.org>