ARM: dts: imx6qdl-kontron-samx6i: fix board reset

[ Upstream commit b972d6b3b46345023aee56a95df8e2c137aa4ee4 ]

On i.MX6 the board is reset by the watchdog. But in turn to do a
complete board reset, we have to assert the WDOG_B output which is
routed also to the CPLD which then do a complete power-cycle of the
board.

Fixes: 21252127 ("ARM: dts: imx6qdl-kontron-samx6i: add Kontron SMARC SoM Support")
Signed-off-by: Michael Walle <mwalle@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>