drm/xe/display: clean up a lot of cruft from compat i915_drv.h

There's a bunch of unused cruft. Just throw away.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/d773f26cced0b376a30a6cb1e38c9581b469d8cf.1712345787.git.jani.nikula@intel.com


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