Patch merged into coreboot/master: build system: don't try to add cbfs-files with no backing file

the following patch was just integrated into master:
commit 1eee076269ce0dbde1a858c67dc86665a656b004
Author: Patrick Georgi 
Date:   Wed Nov 25 18:59:54 2015 +0100

build system: don't try to add cbfs-files with no backing file

Change-Id: Idd05a552762be92d0d93b357b96442b25a614757
    Signed-off-by: Patrick Georgi 
    Reviewed-on: https://review.coreboot.org/12537
    Tested-by: build bot (Jenkins)
    Reviewed-by: Martin Roth

See https://review.coreboot.org/12537 for details.

-gerrit