drm/xe: Convert to USM lock to rwsem

Remove contention from GPU fault path for ASID->VM lookup.

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240918054436.1971839-1-matthew.brost@intel.com