Patch merged into coreboot/master: build system: really disable building CrEC when not needed

the following patch was just integrated into master:
commit 14caed85e121ca623d0ec4b9fba6d5bb64c8c46b
Author: Patrick Georgi 
Date:   Thu May 12 15:13:23 2016 +0200

build system: really disable building CrEC when not needed

Enable users to set the EC_EXTERNAL_FIRMWARE config flag, and actively
    ignore anything related to EC firmware board names if enabled.

BUG=none
    BRANCH=none
    CQ-DEPEND=CL:344540
    TEST=emerge-samus coreboot works

Change-Id: I02aa1e4bc0c98300105b83a12979e9368a40cbcf
    Signed-off-by: Martin Roth 
    Original-Commit-Id: 4f0b6fd10aa89fbb38bdebf14b8a82d52e9ee233
    Original-Change-Id: I39c3038d059ec3d7710b864061fcf83b8d6d4d13
    Original-Signed-off-by: Patrick Georgi 
    Original-Reviewed-on: https://chromium-review.googlesource.com/345584
    Original-Reviewed-by: Aaron Durbin 
    Original-Commit-Queue: Martin Roth 
    Original-Trybot-Ready: Martin Roth 
    Original-Tested-by: Martin Roth 
    Reviewed-on: https://review.coreboot.org/15938
    Tested-by: build bot (Jenkins)
    Reviewed-by: Patrick Georgi

See https://review.coreboot.org/15938 for details.

-gerrit