ARM: dts: imx6ull-colibri: Add general wakeup key used on Colibri

This adds the possibility to wake the module with an external signal
as defined in the Colibri standard

Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
Acked-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>