dt-bindings: spi: sh-msiof: 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>
Link: https://lore.kernel.org/r/1570178133-21532-3-git-send-email-fabrizio.castro@bp.renesas.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/renesas,sh-msiof.yaml

@@ -35,6 +35,7 @@ properties:
       - items:
           - enum:
               - renesas,msiof-r8a774a1      # RZ/G2M
+              - renesas,msiof-r8a774b1      # RZ/G2N
               - renesas,msiof-r8a774c0      # RZ/G2E
               - renesas,msiof-r8a7795       # R-Car H3
               - renesas,msiof-r8a7796       # R-Car M3-W