dt-bindings: serial: atmel,at91-usart: Add SAM9260 compatibles to SAM9X60

Require SAM9260 fallback compatible for SAM9X60, because SAM9X60 is
fully compatible with SAM9260 and Linux driver requires the latter.

Signed-off-by: Sergiu Moga <sergiu.moga@microchip.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220922113347.144383-4-sergiu.moga@microchip.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>