dt-bindings: serial: atmel,at91-usart: add compatible for sam9x7.

Add sam9x7 compatible to DT bindings documentation.
Signed-off-by: Varshini Rajendran <varshini.rajendran@microchip.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240729070636.1990368-1-varshini.rajendran@microchip.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/atmel,at91-usart.yaml

@@ -23,13 +23,20 @@ properties:
           - const: atmel,at91sam9260-dbgu
           - const: atmel,at91sam9260-usart
       - items:
-          - const: microchip,sam9x60-usart
+          - enum:
+              - microchip,sam9x60-usart
+              - microchip,sam9x7-usart
           - const: atmel,at91sam9260-usart
       - items:
           - const: microchip,sam9x60-dbgu
           - const: microchip,sam9x60-usart
           - const: atmel,at91sam9260-dbgu
           - const: atmel,at91sam9260-usart
+      - items:
+          - const: microchip,sam9x7-dbgu
+          - const: atmel,at91sam9260-dbgu
+          - const: microchip,sam9x7-usart
+          - const: atmel,at91sam9260-usart
 
   reg:
     maxItems: 1