configs: stm32mp15: activate DM_REGULATOR_SCMI

Activate the support of SCMI regulator to support the scmi_reg11,
scmi_reg18 and scmi_usb33 regulators present in the scmi device tree of
STMicroelectronics boards with stm32mp15-scmi.dtsi

Fixes: 6cccc8d3 ("ARM: dts: stm32: add SCMI version of STM32 boards (DK1/DK2/ED1/EV1)")
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>