depends: change xlib dependencies

The latest upstream git master requires libXv.so, libX11.so and
libXext.so for enabling xlib. Although this requirement is
currently present only on git master, by examining the changes
it seems to make sense to add it here too.

References
----------
http://git.videolan.org/?p=ffmpeg.git;a=commit;h=0736f32a4facddbd953977ca614a3ee6d8a6e1d7

.SRCINFO

@@ -1,7 +1,7 @@
 pkgbase = ffmpeg-full
 	pkgdesc = Complete solution to record, convert and stream audio and video (all possible features including nvenc, qsv and libfdk-aac)
 	pkgver = 4.0
-	pkgrel = 2
+	pkgrel = 3
 	url = http://www.ffmpeg.org/
 	arch = i686
 	arch = x86_64
@@ -74,7 +74,9 @@ pkgbase = ffmpeg-full
 	depends = mesa
 	depends = sndio
 	depends = sdl2
+	depends = libxv
 	depends = libx11
+	depends = libxext
 	depends = zlib
 	depends = libomxil-bellagio
 	depends = libva