dt-bindings: power: renesas,rzg2l-sysc: Document RZ/G2UL SoC

Add DT binding documentation for SYSC controller found on RZ/G2UL SoC's.
SYSC controller found on the RZ/G2UL SoC is almost identical to one found
on the RZ/G2L SoC's only difference being that the RZ/G2UL has only CA55
core0 reset vector address configuration register.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220315142644.17660-2-biju.das.jz@bp.renesas.com


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