OMAP4: 4430sdp: Register platform device for OMAP4 audio

To avoid breakage in audio support with the coming change
in ASoC machine driver (conversion to platfrom device).

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
CC: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>