ASoC: sun4i-codec: Add support for A31 board level audio routing

The A31 SoC's codec has various inputs, outputs and microphone bias
supplies. These can be routed on the board in different ways, such as:

  - HPCOM may be connected to have the headphone DC coupled.

  - Microphones all use the MBIAS main microphone supply or one mic may
    use the HBIAS supply, which supports headset detection and buttons.

  - Line Out may be routed to an audio jack, or an onboard speaker amp
    with power controls.

Add support for specifying the audio routes in the device tree.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Mark Brown <broonie@kernel.org>