kmsaudiomixer: Add skelleton class

Change-Id: Iabfd46f76609d4d169d80d3e8b3048e10da5dbb0
kmsaudiomixer: Add sink pads

Change-Id: I47d233ac6eb15890188308eb46a2fef6b5984da0
kmsaudiomixer: Interconnect new input audio source to other sources and viceversa

Change-Id: Icb64557ede5c64aa4bf44ff7248ec03ba01c9672