package/qt5quickcontrols: fix licensing information

Since the bump to 5.5.0, the LGPv2.1-with-exception has been dropped,
with only the LGPLv3 or GPLv2 as alternatives.

Drop LGPLv2.1-with-exception.

Add GFDL (GNU Free Documentation License) as it is explicitly referenced
in the source tree.

Fixes:
    http://autobuild.buildroot.org/results/0dc/0dc96010cc81a34d2363eb4fe1a155db0e3769fd/
    http://autobuild.buildroot.org/results/2b0/2b0b4c170dfa0d95c10bf030e6f249b3305dd318/



[Thomas: add version to GFDL specification.]

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Julien CORJON <corjon.j@ecagroup.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>