dt-bindings: i2c: renesas,rcar-i2c: Add r8a779f0 support

Document support for the I2C Bus Interfaces in the Renesas R-Car S4-8
(R8A779F0) SoC, including a new family-specific compatible value for the
R-Car Gen4 family.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>