If the user doesn't specify a TARGET_LIST they get the current
configuration but with spaces and hilarity ensues. This adds some make
magic to turn the TARGET_LIST back into a comma separated list.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

Message-Id: <20180521103504.26432-1-alex.bennee@linaro.org>
Signed-off-by: Fam Zheng <famz@redhat.com>