For codecs that have both SPI and I2C support we need to ensure that we
don't try to make the codec driver built in when I2C is modular since
that won't link.  Do this by creating a helper variable which uses
conditional defaults to pick up the correct value for all combinations.

We don't need to do anything special for I2C-only codecs since a
conditional select passes on the full value for a tristate.
Reported-by: NIngo Molnar <mingo@elte.hu>
Tested-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>