ARM: OMAP: twl-common: Add helper function to register the omap-twl4030 audio driver

Since several OMAP3 based boards will be using the unified simple audio
driver it is better to not have duplicated code in the board files for this
purpose.
Board files can call omap_twl4030_audio_init(); to set up the needed device
for the audio support.

For example:
omap_twl4030_audio_init("omap3beagle", 26000000);

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>