dt-bindings: arm: renesas: Document Renesas RZ/V2M System Configuration

Add DT binding documentation for System Configuration (SYS) found on
RZ/V2M SoC's.

SYS block contains the SYS_VERSION register which can be used to retrieve
SoC version information.

Signed-off-by: Phil Edworthy <phil.edworthy@renesas.com>
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221116102140.852889-2-biju.das.jz@bp.renesas.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>