qt: add font license information

With this implementation, the different licenses will be separated with
<space><comma>. This is not nice, but to avoid it a pretty ugly construct
is needed:

QT_LICENSE = $(shell echo $(QT_LICENSE_BITS) | sed 's% , %, %g')

Since the <space><comma> is just a minor nuisance, we're not going to that kind
of complexity.

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>