lavd: add categories to device implementations

libavdevice/alsa-audio-dec.c

libavdevice/alsa-audio-enc.c

libavdevice/bktr.c

libavdevice/caca.c

libavdevice/decklink_enc_c.c

libavdevice/dshow.c

libavdevice/dv1394.c

libavdevice/fbdev_dec.c

libavdevice/fbdev_enc.c

libavdevice/iec61883.c

libavdevice/jack_audio.c

libavdevice/lavfi.c

libavdevice/libcdio.c

libavdevice/libdc1394.c

libavdevice/openal-dec.c

libavdevice/opengl_enc.c

libavdevice/oss_audio.c

libavdevice/pulse_audio_dec.c

libavdevice/pulse_audio_enc.c

libavdevice/sdl.c