With multiboard support the compiletime generated BOARDINFO string
gets more and more meaningless. This removes it from Kconfig and
replaces it with a variable that can be set at boardlevel.

Also many boards have a standard setting for the hostname in the
environment. This patch also moves the standard to C code by calling
barebox_set_hostname().

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Having the board config file in /env/init has the problem that
the settings in /env/config are overwritten in the init sequence.

This moves the config-board files to /env/ and sources them explicitly
from /env/bin/init before sourcing /env/config

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>