arm64: dts: freescale: imx8mm-verdin: replace sleep-moci hog with regulator

The Verdin family has a signal called sleep-moci which can be used to
turn off peripherals on the carrier board when the SoM goes into
suspend. So far we have hogged this signal, which means the peripherals
are always on and it is not possible to add peripherals that depend on
the sleep-moci to be on. With this change, we replace the hog with a
regulator so that peripherals can add their own regulators that use the
same gpio. Carrier boards that allow peripherals to be powered off in
suspend can disable this regulator and implement their own regulator to
control the sleep-moci.

Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>
Reviewed-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>