dt-bindings: i2c: renesas,iic: Document r8a774e1 support

Document IIC controller for RZ/G2H (R8A774E1) SoC, which is compatible
with R-Car Gen3 SoC family.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Marian-Cristian Rotariu <marian-cristian.rotariu.rb@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>