Manually resolve the conflict between the new enum drm property
helpers in drm-next and the new "force-dvi" option that the "audio" output
property gained in drm-intel-next.

While resolving this conflict, switch the new drm_prop_enum_list to
use the newly introduced enum defines instead of magic values.

Conflicts:
	drivers/gpu/drm/i915/intel_modes.c
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>