dt-bindings: i2c: rcar: Add r8a774c0 support

Document RZ/G2E (R8A774C0) I2C compatibility with the relevant device
dt-bindings.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>