SDCA Improvements

Merge series from Charles Keepax <ckeepax@opensource.cirrus.com>:

Another fairly mixed bag of small SDCA fixes/improvements. Fix one DisCo
property that was treated as mandatory but is actually not present in
the first version of the specification. Fix the counting of routes for
SU/GE DAPM widgets, this currently makes assumptions that are not
guaranteed to be true which can result in too many/few DAPM routes.

Then finally a couple improvements to the volume controls, simplify the
mapping between ALSA and SDCA volumes and pull the volume stuff back
into the SDCA code. It just wasn't sitting right with me that it was
being handled in the ASoC core given it is unlikely to ever see any
reuse outside of SDCA.

diff --cc include/sound/soc.h
Simple merge