dt-bindings: soc: renesas: Document SYS for RZ/V2N SoC

Add the RZ/V2N (R9A09G056) variant to the existing RZ/V2H(P) System
Controller (SYS) binding, as both IPs are very similar.

However, they have different SoC IDs, and the RZ/V2N does not have
PCIE1 configuration registers, unlike the RZ/V2H(P) SYS IP. To handle
these differences, introduce a new compatible string
`renesas,r9a09g056-sys`.

Signed-off-by: Lad Prabhakar <[e-mail]>
Acked-by: Rob Herring (Arm) <[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/soc/renesas/renesas,r9a09g057-sys.yaml

···
     items:
       - enum:
           - renesas,r9a09g047-sys # RZ/G3E
+          - renesas,r9a09g056-sys # RZ/V2N
           - renesas,r9a09g057-sys # RZ/V2H
 
   reg: