MAKEALL: fix a bug to use CROSS_COMPILE_<ARCH>

Commit 27af930e changed the boards.cfg format but
missed to change get_target_arch() fuction.
This commit adjusts it for CROSS_COMPILE_<ARCH>
to work correctly.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>

MAKEALL

@@ -571,7 +571,7 @@ get_target_arch() {
 	local target=$1
 
 	# Automatic mode
-	local line=`egrep -i "^[[:space:]]*${target}[[:space:]]" boards.cfg`
+	local line=`awk '\$7 == "'"$target"'" { print \$0 }' boards.cfg`
 
 	if [ -z "${line}" ] ; then echo "" ; return ; fi