dt-bindings: usb: renesas_usbhs: Add r8a774b1 support

Document RZ/G2N (R8A774B1) SoC bindings.
Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/1570531132-21856-4-git-send-email-fabrizio.castro@bp.renesas.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/renesas,usbhs.txt

@@ -8,6 +8,7 @@ Required properties:
 	- "renesas,usbhs-r8a7745" for r8a7745 (RZ/G1E) compatible device
 	- "renesas,usbhs-r8a77470" for r8a77470 (RZ/G1C) compatible device
 	- "renesas,usbhs-r8a774a1" for r8a774a1 (RZ/G2M) compatible device
+	- "renesas,usbhs-r8a774b1" for r8a774b1 (RZ/G2N) compatible device
 	- "renesas,usbhs-r8a774c0" for r8a774c0 (RZ/G2E) compatible device
 	- "renesas,usbhs-r8a7790" for r8a7790 (R-Car H2) compatible device
 	- "renesas,usbhs-r8a7791" for r8a7791 (R-Car M2-W) compatible device