drm/i915: Move the port sync DP_TP_CTL stuff to the encoder hook

drm/i915: Move the port sync DP_TP_CTL stuff to the encoder hook

Move the final DP_TP_CTL frobbing of port sync to the master
encoder's enable hook. Now neatly out of sight from the high level
modeset code.

And thus we've eliminated all the special casing of port sync
in the high level modeset code.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200313164831.5980-14-ville.syrjala@linux.intel.com
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>