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/Kconfig b/sound/Kconfig
index c710ce2..5a240e0 100644
--- a/sound/Kconfig
+++ b/sound/Kconfig
@@ -76,6 +76,8 @@
 
 source "sound/pci/Kconfig"
 
+source "sound/hda/Kconfig"
+
 source "sound/ppc/Kconfig"
 
 source "sound/aoa/Kconfig"