remove EARLY_INIT and EARLY_CONSOLE support ...

Bitrotted over time and nearly unused, so remove it.

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

move version_string to seperate file ...

In a noninteractive environment barebox will be compiled without
command support. So move version_string to a seperate file which
is compiled unconditionally.
Also, display the banner when the simple console support is used.

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