ASoC: Register platform DAIs

Register all platform DAIs with the core.  In line with current behaviour
this is done at module probe time rather than when the devices are probed
(since currently that only happens as the entire ASoC card is registered
except for those drivers that currently implement some kind of hotplug).
Since the core currently ignores DAI registration this has no practical
effect.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>