Zodiac Inflight Innovations RAVE Supervisory Processor

RAVE Supervisory Processor communicates with SoC over UART. It is
expected that its Device Tree node is specified as a child of a node
corresponding to UART controller used for communication.

Required parent device properties:

 - compatible: Should be one of:
	- "zii,rave-sp-niu"
	- "zii,rave-sp-mezz"
	- "zii,rave-sp-esb"
	- "zii,rave-sp-rdu1"
	- "zii,rave-sp-rdu2"

 - current-speed: Should be set to baud rate SP device is using

RAVE SP consists of the following sub-devices:

Device				 Description
------				 -----------
rave-sp-wdt			: Watchdog
rave-sp-nvmem			: Interface to onboard EEPROM
rave-sp-backlight		: Display backlight
rave-sp-hwmon			: Interface to onboard hardware sensors
rave-sp-leds			: Interface to onboard LEDs
rave-sp-input			: Interface to onboard power button

Example of usage:

	rdu {
		compatible = "zii,rave-sp-rdu2";
		current-speed = <1000000>;

		watchdog {
			compatible = "zii,rave-sp-watchdog";
		};
	};