usb: dwc2: Add definitions for new registers

New registers were added to dwc otg core.

GREFCLK - This register used to control ref_clk parameters.

GINTSTS2 - New WKUP_ALERT interrupt was added.

GINTMSK2 - Mask register for GINTSTS2.

Acked-by: Minas Harutyunyan <hminas@synopsys.com>
Signed-off-by: Grigor Tovmasyan <tovmasya@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>