dt-bindings: serial: rockchip: add rockchip,rk3128-uart

Add rockchip,rk3128-uart compatible string.

Signed-off-by: Johan Jonker <[e-mail]>
Acked-by: Jamie Iles <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml

···
               - rockchip,rk1808-uart
               - rockchip,rk3036-uart
               - rockchip,rk3066-uart
+              - rockchip,rk3128-uart
               - rockchip,rk3188-uart
               - rockchip,rk3288-uart
               - rockchip,rk3308-uart