Clean up the driver with the new managed buffer allocation API.
The hw_params callback became superfluous and dropped.
The hw_free callback still remains because of the substream
deactivation sync call.

Link: https://lore.kernel.org/r/20191209094943.14984-66-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>