drm/i915: only disable DDI sound if intel_crtc->eld_vld

We already have the same check on intel_enable_ddi. This patch
prevents "unclaimed register" messages when the power well is
disabled.

V2: Reset intel_crtc->eld_vld to false after the mode_set function.
V3: Add both "type != INTEL_OUTPUT_EDP" requested.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>