ASoC: Add WM8962 microphone bias control

We unconditionally require SYSCLK since while only microphone detection
specifically requires SYSCLK any actual use case would enable it via
some other means but microphone detection may have nothing active other
than the bias itself.

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