dt-bindings: arm: at91: Add info on sam9x60 curiosity

Adding the sam9x60 curiosity board from Microchip into the atmel AT91 board
description yaml file.

Signed-off-by: Durai Manickam KR <durai.manickamkr@microchip.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20230207110651.197268-8-durai.manickamkr@microchip.com