dt-bindings: i2c: rcar: Add r8a77470 support

Although the I2C IP found in the RZ/G1C is not exactly the same
as the one found in the R-Car Gen2 family or R-Car Gen3 family,
it can still be considered as compatible with R-Car Gen2 from
a software perpective.
This patch therefore documents the SoC specific compatible string,
and the compatibility with Gen2 fallback is retained.
Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Biju Das <biju.das@bp.renesas.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

Documentation/devicetree/bindings/i2c/i2c-rcar.txt

@@ -4,6 +4,7 @@ Required properties:
 - compatible:
 	"renesas,i2c-r8a7743" if the device is a part of a R8A7743 SoC.
 	"renesas,i2c-r8a7745" if the device is a part of a R8A7745 SoC.
+	"renesas,i2c-r8a77470" if the device is a part of a R8A77470 SoC.
 	"renesas,i2c-r8a774a1" if the device is a part of a R8A774A1 SoC.
 	"renesas,i2c-r8a7778" if the device is a part of a R8A7778 SoC.
 	"renesas,i2c-r8a7779" if the device is a part of a R8A7779 SoC.