ARM: dts: imx6q-ba16: use wdog external reset

The BA16 module has a PMIC that uses the WDOG_B output from iMX6 to
reset the system on a watchdog timeout. Configure the watchdog to assert
the external reset signal (WDOG_B) using fsl,ext-reset-output property.

Signed-off-by: Akshay Bhat <akshay.bhat@timesys.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>