msm: kgsl: Improve GPU idle power

The GPU is usually clockgated when idle. Introduce a
new state which removes the pm_qos vote so that CPU
can enter low power modes.

Change-Id: Ibae207bb436fac91d30e67f91a20b1248ee8a198
Signed-off-by: Suman Tatiraju <sumant@codeaurora.org>