ARM: dts: stm32: update SCMI dedicated file

The PWR regulators don't need be removed as they are already deactivated.
This patches is a alignment with the accepted patch in Linux device tree
in commit a34b42f8690c ("ARM: dts: stm32: fix pwr regulators references
to use scmi").

Fixes: 69ef98b2 ("ARM: dts: stm32mp15: alignment with v5.19")
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>