dt-bindings: i2c: i2c-rk3x: Document Rockchip RV1126

Document compatible string for Rockchip RV1126 SoC.

Signed-off-by: Jagan Teki <jagan@edgeble.ai>
Acked-by: Rob Herring <robh@kernel.org>
[wsa: rebased]
Signed-off-by: Wolfram Sang <wsa@kernel.org>