drm/i915: add DP support in LPE audio mode

If DisplayPort is detected, pass flag and link rate to audio driver

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Acked-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>