drm/i915: Add locks around audio component bind/unbind

This will make sure that audio callbacks do not race with
component bind/unbind.

[Note: this is an update patch to commit [51e1d83c: drm/i915: Call
 audio pin/ELD notify function] where I mistakenly applied the older
 version.  Jani and Daniel's review tags were to the latest version,
 so I add them below, too -- tiwai]

Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Takashi Iwai <tiwai@suse.de>