ALSA: hda - Make snd_hda_bus_type public

Define the common hd-audio driver and device types to bind over
snd_hda_bus_type publicly.  This allows to implement other type of
device and driver code over hd-audio bus.

Now both struct hda_codec and struct hda_codec_driver inherit these
new struct hdac_device and struct hdac_driver, respectively.

The bus registration is done in subsys_initcall() to assure it
before any other driver registrations.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/pci/hda/Kconfig b/sound/pci/hda/Kconfig
index 7f0f2c5..a5ed1c1 100644
--- a/sound/pci/hda/Kconfig
+++ b/sound/pci/hda/Kconfig
@@ -5,6 +5,7 @@
 	select SND_PCM
 	select SND_VMASTER
 	select SND_KCTL_JACK
+	select SND_HDA_CORE
 
 config SND_HDA_INTEL
 	tristate "HD Audio PCI"