ENGR00170751 Enable clock gating while gpu core comes to idle

ENGR00170751 Enable clock gating while gpu core comes to idle

-Correct gc355 initial power state to poweroff.
-Separate clock gating operation in function gckOS_SetGPUPower().
-Turn on clock while suspend GPU cores.
-Remove clock switch in drv_open().

Signed-off-by: Loren Huang <b02279@freescale.com>
Acked-by: Lily Zhang