dt-bindings: at91rm9260-rtt: add microchip,sama7d65-rtt

Add SAMA7D65 RTT compatible to DT bindings documentation.

Signed-off-by: Ryan Wanner <[e-mail]>
Acked-by: Rob Herring (Arm) <[e-mail]>
Link: https://lore.kernel.org/r/183[e-mail]
Signed-off-by: Alexandre Belloni <[e-mail]>

Documentation/devicetree/bindings/rtc/atmel,at91sam9260-rtt.yaml

···
           - enum:
               - microchip,sam9x60-rtt
               - microchip,sam9x7-rtt
+              - microchip,sama7d65-rtt
           - const: atmel,at91sam9260-rtt
       - items:
           - const: microchip,sama7g5-rtt