ST LPM Device
-------------

Required properties:
- compatible: should be "st,lpm" for non 407 family SoCs, while it
	      should be "st,stih407-family-lpm" as well as "st,lpm"
	      for 407-family SoCs.
- reg: There are 4 address-size list property. The first one refer to
       the base of the SBC controller. The second one refer to the
       mailbox address and size. Third one refer to the
       configuration registers and the last one refer to the pmem area
       where normally the LPM-f/w has to be loaded and ran from.
- reg-names: Should list the registers names
- interrupts: Standrard interrupt line and type description.

- gpios: A list property, first cell containing the phandle to the gpio
	 port and the second one describes the pin number, that is passed
	 as a parameter to the phandle. This is the gpio pin that is used
	 to switch on/off the SoC power domain by the SBC controller.

- st,lmi-ret-gpio: As the name suggests, this describes the list property
		   describing the gpio pin responsible for lmi retention
		   during the CPS. The first cell contains the phandle to the
		   gpio port and the second one describes the pin number.
- st,fw_name : Should contains the LPM Firmware name

Properties such as compatible, reg, interrupts, st,fw_name typically goes to
the chip description DT file, while gpios and st,lmi-ret-gpio typically goes
to the board description DT file. 

Example:
	lpm:stm-lpm@9400000 {
		compatible = "st,stih407-family-lpm", "st,lpm";
		reg = <0x9400000 0xa0000>,
		<0x94b4000 0x400>,
		<0x94b5100 0x100>,
		<0x020000 0x0>;
		reg-names = "base", "mailbox", "confreg", "pmem";
		interrupts = <GIC_SPI 144 IRQ_TYPE_NONE>;
		st,fw_name = "lpm-fw-STiH407.elf";
		status = "disabled";
	};

	lpm:stm-lpm@9400000 {
		status = "okay";
		gpios = <&PIO3 2>;
		st,lmi-ret-gpio = <&PIO5 2>;
	};
