buildroot

perl-gd: fix build of native part

EUMM don't find .xs file in subdirectory (only .pm files are handled)
So, let move lib/GD.xs in the root directory.

Signed-off-by: Francois Perrad <francois.perrad@gadz.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>