usb: dwc2: Backup and restore PCGCCTL1 register

Backup PCGCCTL1 register when entering hibernation mode and
restore it after exiting from hibernation, to keep active ACG
feature.

Signed-off-by: Razmik Karapetyan <razmik@synopsys.com>
Signed-off-by: Grigor Tovmasyan <tovmasya@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>