ASoC: Remove unused DAPM_DOUBLE control types

There are no users of these and it's not clear what they would do given
the mono flow modelling which DAPM does. If need arises we can add them
again.

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