drm/xe: Document structures for device query

This adds documentation to the various structures used to query
memory, GTs, topology, engines, and so on. It includes a functional
code snippet to query engines.

v2:
  - Rebase on drm-xe-next
  - Also document structures related to drm_xe_device_query, changed
    pseudo code to snippet (Lucas De Marchi)
v3:
  - Move changelog to commit
  - Fix warnings showed only using dim checkpath

Reported-by: Oded Gabbay <ogabbay@kernel.org>
Link: https://lists.freedesktop.org/archives/intel-xe/2023-May/004704.html


Signed-off-by: Francois Dugast <francois.dugast@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>