[ALSA] IEC958 definitions for consumer status channel, byte 4

Added definition for byte 4 of SPDIF channel status, according to
second edition of IEC 60958-3 (consumer) spec.

Signed-off-by: Pawel MOLL <pawel.moll@st.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>