drm/i915: Convert intel_hdmi to use atomic state

This is the last connector still looking at crtc->config. Fix this.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1478609742-13603-7-git-send-email-maarten.lankhorst@linux.intel.com