arm/dts: omap4-sdp: Enable audio support via device tree

On OMAP4 SDP the audio setup includes the twl6040 codec and digital
microphones.

Since OMAP4 SDP is a reference board it has all possible audio interfaces
connected. This information is passed via the ti,audio-routing
property.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>