ASoC: SOF: topology: simplify kcontrol names with

Merge series from Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>:

The use of the widget name as a prefix for the kcontrol name is quite
useful in the case of multiple pipelines going to the same endpoint,
but it's overkill in simpler cases.

This patchset extends the existing DAPM code to drop the widget name
prefix and make the kcontrol names simpler when there's no possible
ambiguity, e.g.  "gain.2.1 Main Playback Volume" becomes just "Main
Playback Volume".