ALSA: hda - allow codecs to access the i915 pin/ELD callback

This lets the interested codec be notified when an i915 pin/ELD
event happens.

[tiwai: Fixed a trivial build error for CONFIG_SND_HDA_I915=n]

Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>