configure: select buffersink_filter when ffplay is enabled

buffersink_filter is a strong requirement for compiling ffplay.
Fixes ffplay compilation with --disable-everything --disable-ffmpeg.

configure

@@ -1517,7 +1517,7 @@ postproc_deps="gpl"
 ffmpeg_deps="avcodec avformat swscale"
 ffmpeg_select="buffer_filter buffersink_filter"
 ffplay_deps="avcodec avformat swscale sdl"
-ffplay_select="rdft"
+ffplay_select="buffersink_filter rdft"
 ffprobe_deps="avcodec avformat"
 ffserver_deps="avformat ffm_muxer fork rtp_protocol rtsp_demuxer"
 ffserver_extralibs='$ldl'