give nice output when generating barebox.bin and barebox.S
As a side effect don't build barebox.S when barebox.bin is updated. I
didn't manage to keep the old behaviour and I consider it cleaner this
way.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>