usb: dwc2: Add host/device hibernation functions

Add host/device hibernation functions which must be wrapped
by core's  dwc2_enter_hibernation()/dwc2_exit_hibernation()
functions.

Make dwc2_backup_global_registers dwc2_restore_global_register
non-static to use them in both host/gadget sides.

Added function names:
dwc2_gadget_enter_hibernation()
dwc2_gadget_exit_hibernation()
dwc2_host_enter_hibernation()
dwc2_host_exit_hibernation()

Signed-off-by: Vardan Mikayelyan <mvardan@synopsys.com>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Artur Petrosyan <arturp@synopsys.com>
Signed-off-by: Minas Harutyunyan <hminas@synopsys.com>
Signed-off-by: Grigor Tovmasyan <tovmasya@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>