ALSA: hda - Add documentation for codec specific mixer controls of Analog codecs

* Channel Mode
This is an enum control to change the surround-channel setup,
appears only when the surround channels are available.
It gives the number of channels to be used, "2ch", "4ch" abd "6ch".
According to the configuration, this also controls the
jack-retasking of multi-I/O jacks.

* Independent HP
When this enum control is enabled, the headphone output is routed
from an individual stream (the third PCM such as hw:0,2) instead of
the primary stream.

Signed-off-by: Raymond Yau <[e-mail]>
Signed-off-by: Takashi Iwai <[e-mail]>

Documentation/sound/alsa/HD-Audio-Controls.txt

···
 
 * Auto-Mute Mode
   See Reatek codecs.
+
+
+Analog codecs
+--------------
+
+* Channel Mode
+  This is an enum control to change the surround-channel setup,
+  appears only when the surround channels are available.
+  It gives the number of channels to be used, "2ch", "4ch" and "6ch".
+  According to the configuration, this also controls the
+  jack-retasking of multi-I/O jacks.
+
+* Independent HP
+  When this enum control is enabled, the headphone output is routed
+  from an individual stream (the third PCM such as hw:0,2) instead of
+  the primary stream.