dt-bindings: i2c: i2c-rk3x: Add compatible string for RK3528

Document I2C controllers integrated in RK3528, which are compatible with
the RK3399 variant.

Signed-off-by: Yao Zi <[e-mail]>
Reviewed-by: Heiko Stuebner <[e-mail]>
Acked-by: Conor Dooley <[e-mail]>
Reviewed-by: Andi Shyti <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Andi Shyti <[e-mail]>

Documentation/devicetree/bindings/i2c/i2c-rk3x.yaml

···
               - rockchip,px30-i2c
               - rockchip,rk3308-i2c
               - rockchip,rk3328-i2c
+              - rockchip,rk3528-i2c
               - rockchip,rk3562-i2c
               - rockchip,rk3568-i2c
               - rockchip,rk3576-i2c