aoc/alsa: support aec ref source selection for voice/voip call

This is to support selecting a differennt aec ref signal for echo
cancellation. For example, on some device, the mic input signal is from
the builtin pdm mic, but the audio playback signal might be sent to
a usb device.

Usage example:
	Set the reference soruce as default:
	tinymix "FT AEC Reference Source" Default

		tinymix "FT AEC Reference Source"
		AEC Reference Source: >Default SPEAKER USB BT

        Set the reference soruce as USB playback:
		tinymix "FT AEC Reference Source" USB

		tinymix "FT AEC Reference Source"
		AEC Reference Source: Default SPEAKER >USB BT

Bug: 205648059

Signed-off-by: Xinhui Zhou <zxinhui@google.com>
Change-Id: I826d988874c2272cb857debdd4db98f9b2241e72