coreboot: require coreboot-sdk

We're removing the common i686-pc-linux-gnu from the SDK.

BUG=b:187786439
TEST=CQ passes

Change-Id: I795bfbda7e58f87229c9a071c6eeafd8e1f0a624
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/3370542
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
1 file changed