ASoC: da7210: Add support for line out and DAC

ASoC: da7210: Add support for line out and DAC

DA7210 has three line outputs. OUT1 Left, OUT1 Right and OUT2 (mono).
This patch adds support for gain controls for these three line outs.
It also adds support for overall DAC gain control.

Signed-off-by: Ashish Chavan <ashish.chavan@kpitcummins.com>
Signed-off-by: David Dajun Chen <dchen@diasemi.com>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>