ARM: OMAP4+: omap2plus_defconfig: Enable audio via TWL6040 as module

Boards supported upstream all use TWL6040 as audio codec, enable the common
ASoC machine driver by default for them.

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