ASoC: OMAP: Select OMAP pin multiplexing when using Nokia N810 ASoC drivers

N810 bootloader muxes I2S pins for OMAP2420 EAC block while N810 ASoC
drivers are using McBSP block so the kernel have to change configuration
runtime.

Author has not seen problems using kernel pin multiplexing on N810 but very
many times unworking audio after forgotten to enable it and spending
15 minutes each time to figure it out again...

This change makes it easier for other users as well. If problems arise, then
they are better to find and fix in OMAP pin multiplexing framework.

Signed-off-by: Jarkko Nikula <jarkko.nikula@nokia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>