dt-bindings: serial: Move renesas,rzn1-uart into the snps-dw-apb-uart binding

The renesas,rzn1-uart binding only differs in compatible string from the
snps-dw-apb-uart binding. Move it there, converting it to json-schema in
the process.

Cc: Phil Edworthy <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: [e-mail]
Reviewed-by: Simon Horman <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/devicetree/bindings/serial/renesas,rzn1-uart.txt

···
-Renesas RZ/N1 UART
-
-This controller is based on the Synopsys DesignWare ABP UART and inherits all
-properties defined in snps-dw-apb-uart.txt except for the compatible property.
-
-Required properties:
-- compatible : The device specific string followed by the generic RZ/N1 string.
-   Therefore it must be one of:
-   "renesas,r9a06g032-uart", "renesas,rzn1-uart"
-   "renesas,r9a06g033-uart", "renesas,rzn1-uart"

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

···
     oneOf:
       - items:
           - enum:
+              - renesas,r9a06g032-uart
+              - renesas,r9a06g033-uart
+          - const: renesas,rzn1-uart
+      - items:
+          - enum:
               - rockchip,px30-uart
               - rockchip,rk3036-uart
               - rockchip,rk3066-uart