asoc: routing: add afe loopback for FM on kona

Add support for AFE loopback between DMA backends
and tertiary mi2s tx on Kona.
This is required for FM playback usecase.

Change-Id: Idc0a1afc522365d15f3cdf28f01ea49f5c399850
Signed-off-by: Meng Wang <mengw@codeaurora.org>