selftests: Makefile: fix for loops in targets to run silently

Fix for loops in targets to run silently to avoid cluttering the test
results.

Suppresses the following from targets: e.g run from breakpoints

for TARGET in breakpoints; do		\
	BUILD_TARGET=$BUILD/$TARGET;	\
	mkdir $BUILD_TARGET  -p;	\
	make OUTPUT=$BUILD_TARGET -C $TARGET;\
done;

Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>