The time to suspend a single codec may be several hundreds of ms. When runtime
power saving is disabled, driver suspend time can be long especially when there
are more than one codec on the bus.

To reduce driver suspend time, this patch creates a work queue for the bus, and
suspends the codecs in parallel if there are multiple codecs on the bus.

[fixed cosmetic issues by tiwai]
Signed-off-by: Mengdong Lin <mengdong.lin@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>