ALSA: hda/sigmatel - Allow auto-switching for dock line-in of HP laptops

Many HP laptops with STAC codecs have a docking station port and BIOS
sets the pins for the input on the dock as a line in.  Because the
generic parser doesn't handle a line in pin as auto-switchable, this
resulted in the manual capture source selection on these laptops.

However, from the usability POV, the automatic switching is easier.
This patch adds the line_in_auto_switch hint in the fixup function for
these laptops.  Even if no dock port is present, this should be
harmless as the generic parser allows the auto-switching only in a
limited situation (all three pins are located in different
positions).

Signed-off-by: Takashi Iwai <tiwai@suse.de>