qt5x11extras: fix license information

This commit fixes several problems with the license information of
qt5x11extras:

 - With the latest version update the legacy version files
   LICENSE.GPLv2 LICENSE.GPLv3 and LICENSE.LGPLv3 were removed, use
   the new ones LICENSE.GPL2 LICENSE.GPL3 and LICENSE.LGPL3 instead.

   Fixes:

   http://autobuild.buildroot.net/results/238bb74f23d7a11516eac088da3188d463abac5a



 - Hashes for some licenses files for the 5.6.3 version were missing.

As part of this, we switch to using per-version hash files entirely.

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>