ALSA: pcm: Embed struct device

Like previous patches, at this time we embed the struct device into
PCM object.  However, this needs a bit more caution: struct snd_pcm
doesn't own one device but two, for both playback and capture!  Thus
not struct snd_pcm but struct snd_pcm_str object contains the device.

Along with this change, pcm->dev field is dropped for avoiding
confusion.  It was meant to point to a non-standard parent.  But,
since now we can touch each struct device directly, we can manipulate
the parent field easily there, too.

Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>