libbluray: add optional fontconfig dependency

Fixes:
http://autobuild.buildroot.net/results/dbf/dbfbf09f48e7ec09be34a3a40d3c859b74379eaf/
http://autobuild.buildroot.net/results/3fb/3fb9c077d4fe772774f53c7611b4dcbaad361312/
http://autobuild.buildroot.net/results/f9c/f9c1f3cf8bfa9eeacb7719459c22bdf7dea26ddb/



and more.

Cc: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>