ARM: dts: imx6qdl-apalis: Fix poweroff on Apalis iMX6

ARM: dts: imx6qdl-apalis: Fix poweroff on Apalis iMX6

The current solution for powering off the Apalis iMX6 is not functioning
as intended. To resolve this, it is necessary to power off the
vgen2_reg, which will also set the POWER_ENABLE_MOCI signal to a low
state. This ensures the carrier board is properly informed to initiate
its power-off sequence.

The new solution uses the regulator-poweroff driver, which will power
off the regulator during a system shutdown.

Cc: <stable@vger.kernel.org>
Fixes: 4eb56e26f92e ("ARM: dts: imx6q-apalis: Command pmic to standby for poweroff")
Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>