usb: dwc2: host: enter hibernation during bus suspend

Disable controller power and enter hibernation when usb bus is
suspended. A phy driver is required to disable the power of the
controller and detect remote-wakeup or disconnection since the
controller will not be able to detect these in this state.

Once the phy driver detects bus activity, it must call
usb_hcd_resume_root_hub.

Signed-off-by: Gregory Herrero <gregory.herrero@intel.com>
Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@intel.com>
Tested-by: Robert Baldyga <r.baldyga@samsung.com>
Tested-by: Dinh Nguyen <dinguyen@opensource.altera.com>
Tested-by: John Youn <johnyoun@synopsys.com>
Acked-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>