drm/i915: Fix type1 DVI DP dual mode adapter heuristic for modern platforms

Looks like we never updated intel_bios_is_port_dp_dual_mode() when
the VBT port mapping became erratic on modern platforms. This
is causing us to look up the wrong child device and thus throwing
the heuristic off (ie. we might end looking at a child device for
a genuine DP++ port when we were supposed to look at one for a
native HDMI port).

Fix it up by not using the outdated port_mapping[] in
intel_bios_is_port_dp_dual_mode() and rely on
intel_bios_encoder_data_lookup() instead.

Cc: stable@vger.kernel.org
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/4138
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211025142147.23897-1-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>