STM32 BOOSTER - Booster for ADC analog input switches

Some STM32 devices embed a 3.3V booster supplied by Vdda, that can be used
to supply ADC analog input switches.

Required properties:
- compatible: Should be one of:
  "st,stm32h7-booster"
  "st,stm32mp1-booster"
- st,syscfg: Phandle to system configuration controller.
- vdda-supply: Phandle to the vdda input analog voltage.

Example:
	booster: regulator-booster {
		compatible = "st,stm32mp1-booster";
		st,syscfg = <&syscfg>;
		vdda-supply = <&vdda>;
	};