drm/xe: Update workaround documentation

Bring it up to reality, better documenting the existing batch buffers,
OOB rules and fixing some typos.

Bspec: 60122
Reviewed-by: Stuart Summers <stuart.summers@intel.com>
Link: https://lore.kernel.org/r/20250911-wa-bb-cmds-v4-1-c8f7e48f7eae@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>