intel_sst: Line out support

This patch adds the support for lineout. The
lineout input can be selected as any input channel
by using a new alsa mixer kcontrol.

Signed-off-by: Dharageswari R <dharageswari.r@intel.com>
Signed-off-by: Ramesh Babu K V <ramesh.babu@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>