basemixer: Improve release procedure

Change-Id: I7e288249f3f3ccc5720292e21eb5d83b1efeb79f
mainmixer: Link port with main if there is a main already

Change-Id: I390f95fb3c09be47fef08590b4960f5623ae7bc0
mainmixer: If main port is removed set main port as none

Change-Id: I5d1baabea4f6d74e5e9712443fb578e9f76179ed
mainmixer: Connect ports when main is changed

Change-Id: Ib5981e246642eb1b2a8474307c2c297d206b9a2f
basemixer: Add methods to disconnect pads internally

Change-Id: I323643a485546f4e5f4ffa89dc602d4f3e34591c
mainmixer: Disconnect src pads when main port is removed or set to none

Change-Id: I1eb8f17f8dcaa33df36ca4231a50fe556ad6270f