drm/xe/compat: remove unused platform macros

After refactors, a lot of platform macros have become unused. Remove
them before new users have a chance to pop up.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://lore.kernel.org/r/4507b49ead12c997de4615fa6ec277e666e5226a.1753965351.git.jani.nikula@intel.com


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