ALSA: hda/tas2781: remove sound controls in unbind

Remove sound controls in hda_unbind to make
module loadable after module unload.

Add a driver specific struct (tas2781_hda) to store
the controls.

This patch depends on patch:
ALSA: hda/tas2781: do not use regcache

Fixes: 5be27f1e

 ("ALSA: hda/tas2781: Add tas2781 HDA driver")
CC: stable@vger.kernel.org
Signed-off-by: Gergo Koteles <soyer@irl.hu>
Link: https://lore.kernel.org/r/362aa3e2f81b9259a3e5222f576bec5debfc5e88.1703204848.git.soyer@irl.hu
Signed-off-by: Takashi Iwai <tiwai@suse.de>