Revert "mkconfig: start deprecating Makefile config targets"

This reverts commit 1285a2808a254f3d1a809c1a541f0c0f746e03d7 since the migration
of boards from Makefile to boards.cfg is now complete.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>

doc/feature-removal-schedule.txt

@@ -51,22 +51,6 @@ Who:	Andy Fleming <afleming@freescale.com> and driver maintainers
 
 ---------------------------
 
-What:	boards with xxx_config targets in top level Makefile
-When:	Release v2012.03
-
-Why:	We have a boards.cfg file which the vast majority of boards have
-	converted over to.  Boards that still manually run mkconfig in the
-	top level Makefile are either dead, or the maintainer doesn't care,
-	or they are doing something weird/wrong that should be fixed in a
-	different way, or they need to extend boards.cfg syntax (unlikely).
-
-	In any case, if no one cares about these boards to figure out how
-	to make boards.cfg work, then we'll just punt them.
-
-Who:	Mike Frysinger <vapier@gentoo.org>
-
----------------------------
-
 What:	GPL cleanup
 When:	August 2009
 Why:	Over time, a couple of files have sneaked in into the U-Boot

mkconfig

@@ -29,15 +29,6 @@ if [ \( $# -eq 2 \) -a \( "$1" = "-A" \) ] ; then
 	set ${line}
 	# add default board name if needed
 	[ $# = 3 ] && set ${line} ${1}
-elif [ "${MAKEFLAGS+set}${MAKELEVEL+set}" = "setset" ] ; then
-	# only warn when using a config target in the Makefile
-	cat <<-EOF
-
-	warning: Please migrate to boards.cfg.  Failure to do so will
-	         mean removal of your board in the next release.
-
-	EOF
-	sleep 5
 fi
 
 while [ $# -gt 0 ] ; do