dt-bindings: pinctrl: sh-pfc: Document r8a774b1 PFC support

Document PFC support for the R8A774B1 SoC.
Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Link: https://lore.kernel.org/r/1568881036-4404-8-git-send-email-biju.das@bp.renesas.comSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

Documentation/devicetree/bindings/pinctrl/renesas,pfc-pinctrl.txt

@@ -18,6 +18,7 @@ Required Properties:
     - "renesas,pfc-r8a7745": for R8A7745 (RZ/G1E) compatible pin-controller.
     - "renesas,pfc-r8a77470": for R8A77470 (RZ/G1C) compatible pin-controller.
     - "renesas,pfc-r8a774a1": for R8A774A1 (RZ/G2M) compatible pin-controller.
+    - "renesas,pfc-r8a774b1": for R8A774B1 (RZ/G2N) compatible pin-controller.
     - "renesas,pfc-r8a774c0": for R8A774C0 (RZ/G2E) compatible pin-controller.
     - "renesas,pfc-r8a7778": for R8A7778 (R-Car M1) compatible pin-controller.
     - "renesas,pfc-r8a7779": for R8A7779 (R-Car H1) compatible pin-controller.