Split the monolithc HD-audio driver into several pieces:
 - snd-hda-intel   HD-audio PCI controller driver; loaded via udev
 - snd-hda-codec   HD-audio codec bus driver
 - snd-hda-codec-* Specific HD-audio codec drivers

When built as modules, snd-hda-codec (that is invoked by snd-hda-intel)
looks up the codec vendor ID and loads the corresponding codec module
automatically via request_module().

When built in a kernel, each codec drivers are statically hooked up
before probing the PCI.

This patch adds appropriate EXPORT_SYMBOL_GPL()'s and the module
information for each driver, and driver-linking codes between
codec-bus and codec drivers.

TODO:
  - Avoid EXPORT_SYMBOL*() when built-in kernel
  - Restore __devinit appropriately depending on the condition

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