arm64: dts: imx8mm-verdin: update regulator names

Annotate regulators which are on-module.
Rename usb_otg{1/2}_vbus to USB_{1/2}_EN more in-line with Verdin spec.
Annotate PMIC regulators with information on which BUCK/LDO they are on.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>