ARM: dts: at91: sam9x60: add watchdog node

Add node for watchdog timer.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Link: https://lore.kernel.org/r/1581408369-14469-1-git-send-email-eugen.hristev@microchip.com


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