DT: irqchip: renesas-irqc: document R8A7743/5 support

Renesas  RZ/G SoC have the R-Car gen2 compatible IRQC interrupt controllers.
Document RZ/G1[ME] (also known as R8A774[35]) SoC bindings.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Rob Herring <robh@kernel.org>