ARM: OMAP4: board-4430sdp: Register platform device for digimic codec

OMAP4 SDP/Blaze boards have onboard digital microphones.
Register the platform device for the dmic-codec to be
able to use the microphones.

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