STMicroelectronics STM32 Factory-programmed data device tree bindings

This represents STM32 Factory-programmed read only non-volatile area: locked
flash, OTP, read-only HW regs... This contains various information such as:
analog calibration data for temperature sensor (e.g. TS_CAL1, TS_CAL2),
internal vref (VREFIN_CAL), unique device ID...

Required properties:
- compatible:		Should be one of:
			"st,stm32f4-otp"
			"st,stm32mp15-bsec"
- reg:			Offset and length of factory-programmed area.
- #address-cells:	Should be '<1>'.
- #size-cells:		Should be '<1>'.

Optional Data cells:
- Must be child nodes as described in nvmem.txt.

Example on stm32f4:
	romem: nvmem@1fff7800 {
		compatible = "st,stm32f4-otp";
		reg = <0x1fff7800 0x400>;
		#address-cells = <1>;
		#size-cells = <1>;

		/* Data cells: ts_cal1 at 0x1fff7a2c */
		ts_cal1: calib@22c {
			reg = <0x22c 0x2>;
		};
		...
	};
