ALSA: opti-miro: make miro.h header available outside the alsa directory

Move the miro.h header to the include/sound directory. It can
be used in the Miro PCM20 radio driver (v4l).

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Takashi Iwai <tiwai@suse.de>