arm: dts: verdin-imx8mm/imx8mp: use gpio-hog for sleep moci

arm: dts: verdin-imx8mm/imx8mp: use gpio-hog for sleep moci

In Linux, we allow sleep moci to be turned off when the carrier board
supports it and the system is in suspend. In U-Boot, however, we want
the sleep moci to be always on. So we use a gpio hog and disable the
regulator. This change is necessary because we switched to upstream
device tree files with commit 23fe2def1edf
("verdin-imx8mm/verdin-imx8mp: move imx verdins to OF_UPSTREAM"). A
recent upstream patch removes the gpio hog from the Linux device tree,
so we need to add it to the u-boot dtsi. The following patch will remove
the gpio hog from the Linux device tree:
https://lore.kernel.org/linux-devicetree/20240405160720.5977-1-eichest@gmail.com/
The U-Boot patch can be applied without it and will not break the build.

Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>