The SOF HD-audio bus has its house-made initialization code.  It's
supposedly for making the code independent from HD-audio bus drivers.
However, this is error-prone, and above all, the SOF driver has
already dependency on HD-audio bus driver when CONFIG_SND_SOF_HDA is
set.  That is, if this Kconfig is set, there is no reason to avoid the
call to the proper bus init function.

Also, the ext_ops that is set at bus initialization can be better
handled inside sof_hda_bus_init().  We don't need to refer this
outside the bus initialization.

So this patch addresses these issues:
- sof_hda_bus_init() calls nothing but snd_hdac_ext_bus_init()
  when CONFIG_SND_SOF_HDA is set.  Otherwise some fields are
  initialized locally like before for avoiding the dependency.
- ext_ops is referred inside sof_hda_bus_init().  The ext_ops argument
  of snd_hda_bus_init() is dropped.
Acked-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>