dt-bindings: at91rm9260-rtt: add sam9x7 compatible

Add compatible for SAM9X7 RTT.

Signed-off-by: Varshini Rajendran <varshini.rajendran@microchip.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240223172552.672094-1-varshini.rajendran@microchip.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>