drm/i915/bios: rename display_device_data to intel_bios_encoder_data

Make the naming suitable for exposing to the rest of the driver as an
opaque type. No functional changes.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/cb97c858de6e6afa96092db6d96e685fda006984.1615998927.git.jani.nikula@intel.com