for_each_encoder_on_crtc() is legacy and shouldn't be used by atomic
drivers. Let's throw out intel_trans_dp_port_sel() and replace it
with intel_get_crtc_new_encoder() which looks the atomic state instead.

Since we now have to call intel_get_crtc_new_encoder() during the commit
phase we'll need to plumb in the top level atomic state. The
crtc_state->state pointers are no longer valid at that point.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180518152931.13104-3-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>