ARM: dts: imx: ventana: Add ext watchdog reset

bc677ff4

 adds a device-tree property
to specify that an external watchdog reset is used to reset other
portions of the board and not just the IMX6 SoC.

This adds the property to the proper watchdog as well as the pinmux for
the Gateworks Ventana boards that use this external watchdog reset to
reset the PMIC which will reset all the PMIC power rails and not just
a chip-level IMX6 reset. This helps to work around various system issues
that can cause a hang when coming out of reset.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>