qt: make sure to install all Qt-fonts and true-type-fonts

Qt gained some more qpf-fonts and also provides some true-type-fonts.
Make sure to install them all inclusive ttf-fonts when freetype-support
is enabled. Additionally the empty 'fontdir' file is really not needed.

Signed-off-by: Michael Roth <mroth@nessie.de>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>