vlc: fix build with libvorbis and tremor

vlc: fix build with libvorbis and tremor

Commit 550c42509c203891c47d934b058a19c2fa490973 "package/vlc: fix
linking with tremor" fixed build with BR2_PACKAGE_TREMOR and without
BR2_PACKAGE_LIBVORBIS. However, it breaks build if BR2_PACKAGE_TREMOR
and BR2_PACKAGE_LIBVORBIS are both enabled.
Indeed, by overiding VORBIS_LIBS by -lvorbisidec, link of
codec/.libs/libvorbis_plugin_la-vorbis.o with -lvorbis
failed because VORBIS_LIBS is normally used to save "-logg
-lvorbis -lvorbisenc":
PKG_ENABLE_MODULES_VLC([VORBIS], [], [ogg vorbis >= 1.1 vorbisenc >= 1.1], [Vorbis decoder and encoder], [auto])

So replace fourth patch by an upstreamable patch which uses pkg-config
to set TREMOR_LIBS if tremor is found instead of "hacking" VORBIS_LIBS

Fixes:
 - http://autobuild.buildroot.org/results/85a7bb1996b78dee037d5900b124cbdf5b66a6ac

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>