Patch merged into coreboot/master: u-boot: Make sure targets aren't duplicated

the following patch was just integrated into master:
commit 22aa9e3fcc973dccdbe4f19cad8de6d3146c701f
Author: Martin Roth 
Date:   Mon Feb 22 14:03:13 2016 -0800

u-boot: Make sure targets aren't duplicated

When U-Boot isn't selected as a payload, two of the targets:
    $(project_dir): and $(project_dir)/$(TAG-y) evaluated to the same
    value, generating a make warning when running a clean.  By adding
    additional text to the file that is created, this is avoided.

Gets rid of these warnings:
    Makefile.inc:54: warning: overriding commands for target `u-boot'
    Makefile.inc:37: warning: ignoring old commands for target `u-boot'

Change-Id: I4b4df753612b674b3ccde2a757338840be92d1f2
    Signed-off-by: Martin Roth 
    Reviewed-on: https://review.coreboot.org/13767
    Tested-by: build bot (Jenkins)
    Reviewed-by: Stefan Reinauer

See https://review.coreboot.org/13767 for details.

-gerrit