The Arizona CODECs contain a haptics module providing vibration feedback
support. Implement basic support for this, providing simple start/stop and
signal magnitude control.

Since the output path for haptics is routed through the CODEC audio routing
it is modelled as a signal generator within ASoC, the haptics driver calls
DAPM to start and stop the output drivers. An appropriate output path must
be configured via ALSA to connect the haptics source to the correct output.
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>