drm/i915/bios: throw away unused DVO_* macros

Apparently meant to be additional DEVICE_PORT_* or DVO_PORT_* macros,
but left unused at some point. Remove. No functional changes.

Cc: Animesh Manna <animesh.manna@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/76a1b91bfe05e9e1c04d921b9c4364461f754905.1503600621.git.jani.nikula@intel.com