ALSA: maestro3: Enable docking support for Dell Latitude C810

Enable I2S docking for Dell Latitude C810.
This allows the audio output on C/Port II to work (and probably also
the audio inputs on C/Dock II).

The volume can't be adjusted - none of the mixer controls currently
supported affects the I2S output (they belong to the STAC9721/23 AC'97
codec responsible for the laptop internal connectors & speakers).

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>