Generic reboot mode core map driver

This driver get reboot mode arguments and call the write
interface to stores the magic value in special register
or ram . Then the bootloader can read it and take different
action according the argument stored.

All mode properties are vendor specific, it is a indication to tell
the bootloder what to do when the system reboot, and should be named
as mode-xxx = <magic> (xxx is mode name).

- mode-normal: Normal reboot mode, system reboot with command "reboot".
- mode-recovery: Android Recovery mode, it is a mode to format the device or update a new image.
- mode-bootloader: Android fastboot mode, it's a mode to re-flash partitions on the Android based device.
- mode-loader: A bootloader mode, it's a mode used to download image on Rockchip platform,
	       usually used in development.

Example:
	reboot-mode {
		mode-normal = <BOOT_NORMAL>;
		mode-recovery = <BOOT_RECOVERY>;
		mode-bootloader = <BOOT_FASTBOOT>;
		mode-loader = <BOOT_LOADER>;
	}
