ASoC: core: Try to use regmap if the driver doesn't set up any I/O

Since most new drivers are expected to use regmap and since frequently the
only thing we need to do in the CODEC probe function is configure the I/O
try to initialise the register I/O using regmap if the driver hasn't done
so after probe().

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@ti.com>