drm/i915/bios: Extract intel_bios_encoder_port()

We'll have a few places where we need to do the full (incl. ICL+ DSI)
DVO port->port conversion, so extract the code for that into a helper.

Suggested-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230630155846.29931-6-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>