Add an "-l <num>" argument to abuild that sets the LOGLEVEL variables

Add an "-l <num>" argument to abuild that sets the LOGLEVEL variables
to the specified value.

Only change Config-abuild.lb, as the others are for manual buildtarget
use - adding __LOGLEVEL__ there would kill the build as it isn't
replaced by the actual content.

Signed-off-by: Patrick Georgi <patrick.georgi@coresystems.de>
Acked-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
Acked-by: Stefan Reinauer <stepan@coresystems.de>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@4153 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1