ASoC: Allow disabling of WM835x jack detection

If no report is specified then disable detection. Note that we don't
disable the slow clock, though the power consumption from it should
be negligable. That should be reference counted, ideally through DAPM.

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