Add include to config.g

Add include to config.g

Usage:

include path

path can be relative to the current directory or absolute starting at /src.

I tested it with:

include /config/absolute.lb
include relative.lb

in /src/northbridge/amd/amdk8/Config.lb
which included
   /src/northbridge/amd/amdk8/relatvie.lb
   /src/config/absolute.lb

Signed-off-by: Myles Watson <mylesgw@gmail.com>
Acked-by: Ronald G. Minnich <rminnich@gmail.com>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@4131 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1