AS0C: Add afe_loopback_tx support for apq8009 BE dai

Add afe_loopback_tx dai driver and routing. Add afe_loopback_tx
dai driver and routing driver changes for afe_loopback_tx back
end dai's.

Change-Id: Ia57f335bde5f8a47de0030fbf1cdb784c8821e17
Signed-off-by: Surendar karka <sukark@codeaurora.org>
Signed-off-by: Raja Mallik <rmallik@codeaurora.org>