ALSA: hda - Fix registration of beep input device

The beep input device is registered via input_register_device(), but
this is called in snd_hda_attach_beep_device() where the sound devices
aren't registered yet.  This leads to the binding to non-existing
object, thus results in failure.  And, even if the binding worked
(against the PCI object), it's still racy; the input device appears
before the sound objects.

For fixing this, register the input device properly at dev_register
ops of the codec object it's bound with.  Also, call
snd_hda_detach_beep_device() at dev_disconnection so that it's
detached at the right timing.  As a bonus, since it's called in the
codec's ops, we can get rid of the further call from the other codec
drivers.

Signed-off-by: Takashi Iwai <tiwai@suse.de>