Patch merged into coreboot/master: Makefile: Just error out if no .config exists

the following patch was just integrated into master:
commit 20aa043b449dc68379f4b64c257a066e17fda4b8
Author: Martin Roth 
Date:   Thu Jan 26 10:51:43 2017 -0700

Makefile: Just error out if no .config exists

Currently coreboot runs the 'config' command if no .config file exists.
    This isn't what anyone wants, and is particularly frustrating for tools
    that automate the build, where the build just hangs waiting for input.

Instead, just show an error message and then exit the build.

Change-Id: If9e0c2c26f8273814518589a2f94c5b00fc4cefe
    Signed-off-by: Martin Roth 
    Reviewed-on: https://review.coreboot.org/18245
    Tested-by: build bot (Jenkins)
    Reviewed-by: Nico Huber

See https://review.coreboot.org/18245 for details.

-gerrit