lint: test that labels begin at start-of-line

lint: test that labels begin at start-of-line

Some attempt at enforcing style

Change-Id: Ibbfb86402ecc57e8db6c3857c8e0193085ed4fc2
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/771
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>