package/tvheadend: bump version, add optional dependencies to opus & x265

package/tvheadend: bump version, add optional dependencies to opus & x265

This bump
https://github.com/tvheadend/tvheadend/compare/54e63e3f9af8fdc0d23f61f3cda7fa7b246c1732...303f418e1ac2bb3078f7a974b69f04ab6a56c636
updated the transcoding support already present:
https://github.com/tvheadend/tvheadend/commit/014bb9505e1d7eb6e37e10931dd89ab3b1a0dc01

To avoid these build errors

src/transcoding/codec/codecs/libs/libx26x.c:105:18: fatal error: x264.h: No such file or directory
 #include <x264.h>

src/transcoding/codec/codecs/libs/libx26x.c:213:18: fatal error: x265.h: No such file or directory
 #include <x265.h>

src/transcoding/codec/codecs/libs/libopus.c:23:31: fatal error: opus/opus_defines.h: No such file or directory
 #include <opus/opus_defines.h>

we need to add dependency handling already with this patch and keep the
hard dependency x264 as minimum codec for transcoding but we now need
to enable BR2_PACKAGE_FFMPEG_GPL to enable x264-support also in ffmpeg.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>