We use barebox,state as compatible for the state node. The
barebox,bootstate node serves no purpose with current code base and is
just confusing. Drop it.

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