ARM: dts: imx8mm-verdin: follow changed pmic

The used PMIC has been changed from RHOM BD71837 to NXP PCA9450A.
Adjust the device tree accordingly.
Remove the old ADC node as the ADC has been changed and has no longer
a separate power rail.

Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com>
Signed-off-by: Igor Opaniuk <igor.opaniuk@toradex.com>
Acked-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>