ASoC: topology: Allow a widget to have multiple enum controls

This patch can create multiple enumerated mixer controls for a widget.

Previously topology kernel driver assumes a widget can have only one
emumerated mixer control. We need to remove this restriction for Broxton.
Its firmware modules (widgets) may need multiple enum controls based on
the channel and MIC combination.

No ABI change is needed. The ABI allows a widget to embed multiple
controls.

Reported-by: G Kranthi <gudishax.kranthikumar@intel.com>
Signed-off-by: Mengdong Lin <mengdong.lin@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>