ALSA: hda - Create own device struct for each codec

As the HD-audio is treated individually in each codec driver, it's
more convenient to assign an own struct device to each codec object.
Then we'll be able to use dev_err() more easily for each codec, for
example.

For achieving it, this patch just creates an object "hdaudioCxDy".
It belongs to sound class instead of creating a new bus, just for
simplicity, at this stage.  No pm ops is implemented in the device
struct level but currently it's merely a container.  The PCM and hwdep
devices are now children of this codec device.

Signed-off-by: Takashi Iwai <tiwai@suse.de>