drm/i915: extract intel_edp_init_connector

Because intel_dp_init_connector is too big for my poor little brain.
No functional changes.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Zoltan Nyul <zoltan.nyul@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>