Instead of manual calls of device_create_file() and
device_remove_file(), use static attribute groups with proper
is_visible callbacks for managing the sysfs entries.

This simplifies the code a lot and avoids the possible races.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: http://lkml.kernel.org/r/1423046938-18111-2-git-send-email-tiwai@suse.deSigned-off-by: Borislav Petkov <bp@suse.de>