ARM: dts: at91: sama5d2_ptc_ek: add PB_USER as wakeup source

Add the push button PB_USER as wakeup source

Signed-off-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Link: https://lore.kernel.org/r/20200401221504.41196-3-ludovic.desroches@microchip.com


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