libav: add 10.5

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
angstrom v2014.12: prefer libav 10.5

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
tvheadend: add 3.9

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>