drm/xe/uapi: Document drm_xe_query_config keys

Provide a description of the keys used the struct
drm_xe_query_config info array.

Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/637


Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: José Roberto de Souza <jose.souza@intel.com>
Acked-by: Mateusz Naklicki <mateusz.naklicki@intel.com>
Signed-off-by: Francois Dugast <francois.dugast@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>