drm/i915: move intel_init_audio_hooks inside display

intel_init_audio_hooks() sets up hooks in the display struct and only
makes sense when we have display. Move it inside
intel_init_display_hooks() so it isn't called when we don't have
display.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20210213042756.953007-4-lucas.demarchi@intel.com