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 <phil.edworthy@renesas.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-serial@vger.kernel.org
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -15,6 +15,11 @@ allOf:
 properties:
   compatible:
     oneOf:
+      - items:
+          - enum:
+              - renesas,r9a06g032-uart
+              - renesas,r9a06g033-uart
+          - const: renesas,rzn1-uart
       - items:
           - enum:
               - rockchip,px30-uart