dt-bindings: pinctrl: renesas: Document RZ/V2N SoC

Add documentation for the pin controller found on the Renesas RZ/V2N
(R9A09G056) SoC. The RZ/V2N PFC differs slightly from the RZ/G2L family
and is almost identical to the RZ/V2H(P) SoC, except that the RZ/V2H(P) SoC
has an additional dedicated pin.

To account for this, a SoC-specific compatible string,
'renesas,r9a09g056-pinctrl', is introduced for the RZ/V2N SoC.

Signed-off-by: Lad Prabhakar <[e-mail]>
Reviewed-by: Geert Uytterhoeven <[e-mail]>
Link: https://lore.kernel.org/[e-mail]
Signed-off-by: Geert Uytterhoeven <[e-mail]>

Documentation/devicetree/bindings/pinctrl/renesas,rzg2l-pinctrl.yaml

···
               - renesas,r9a07g044-pinctrl # RZ/G2{L,LC}
               - renesas,r9a08g045-pinctrl # RZ/G3S
               - renesas,r9a09g047-pinctrl # RZ/G3E
+              - renesas,r9a09g056-pinctrl # RZ/V2N
               - renesas,r9a09g057-pinctrl # RZ/V2H(P)
 
       - items:
···
           contains:
             enum:
               - renesas,r9a09g047-pinctrl
+              - renesas,r9a09g056-pinctrl
               - renesas,r9a09g057-pinctrl
     then:
       properties: