ASoC: tpa6130a2: Add stereo DAPM path

New DAPM widgets, and paths to enable both channels at the
same time (for stereo output).
With this path the switch time difference can be avoided
between left and right channels.
The original DAPM paths can be still used, if only one of
TPA's output has been connected to a speaker, but for most of
the cases, switching to the stereo path is better.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>