OLPC XO needs a few special handling.  Now these are implemented as a
fixup to the generic parser.

Obviously, the DC BIAS mode had to be added manually.  This is mainly
implemented in the mic_autoswitch hook, where the mic pins are
overwritten depending on the DC bias mode.  This also required the
override of the mic boost control, since the mic boost is applied only
when the DC mode is disabled.

In addition, the mic pins must be set dynamically at recording time
because these also control the LED.
Signed-off-by: Takashi Iwai <tiwai@suse.de>