gst-ffmpeg: fix build on armv6 without thumb2 (e.g. RaspberryPi)

[Thomas: rename existing patch and the one added by Arnout to follow
the patch naming convention.]

Cc: Marco Trapanese <marcotrapanese@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>