ENGR00252727-2 [GPU]Power on VG core if there is only VG core in SoC

ENGR00252727-2 [GPU]Power on VG core if there is only VG core in SoC

-Power on VG core to makesure VG can be initalized if there is only
VG core in SoC.
-Power off VG core after initalization is done.
-Adjust VG power and clock state to match above changing.

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