ASoC: Support configuration of WM8958 microphone bias analogue parameters

The WM8958 has a different microphone bias architecture to WM8994 so needs
different configuration to WM8994. Support this in platform data.

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