dt-bindings: i2c: Document RZ/V2M I2C controller

Document Renesas RZ/V2M (r9a09g011) I2C controller bindings.

Signed-off-by: Phil Edworthy <phil.edworthy@renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>