ASoC: TWL4030: Change DAPM routings and controls for DACs and PGAs

Restructuring the twl4030 codec's DAPM routing to be able to handle the power
sequences correctly.

The twl4030 codec internal implementation have this order:
DAC -> Analog PGA -> Mixer/Mux

While the ASoC framework expects the following order:
DAC -> Mixer -> Analog PGA

This patch moves the Analog PGA handling from SND_SOC_DAPM_PGA to _MIXER and
adds two levels of mixer to handle the digital and analog loopback
functionality.

Now the analog loopback does not powers on any of the DACs.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Tested-by: Anuj Aggarwal <anuj.aggarwal@ti.com>
Tested-by: Jarkko Nikula <jhnikula@gmail.com>
Tested-by: Misael Lopez Cruz  <x0052729@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>