This adds a new node for reboot modes on LEGO MINDSTORMS EV3. The EV3's
bootloader looks for a magic number in the ARM local RAM and if found,
it will boot into a special firmware update mode where the flash memory
can be written via USB.
This has been testing working using the command:
# systemctl reboot loader
Signed-off-by: David Lechner <david@xxxxxxxxxxxxxx>
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