Previous commit now allows probing barebox,hostfile to be probed from
device tree. Add a barebox state node that shows how to use it. It's not
included by default, same as barebox-libftdi-example.dtsi in the same
directory.

Signed-off-by: Ahmad Fatoum <ahmad@a3f.at>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>