drm/xe: Add documentation for survivability mode

Add survivability mode document to pcode document as it is enabled
when pcode detects a failure.

v2: fix kernel-doc (Lucas)

Signed-off-by: Riana Tauro <riana.tauro@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20250407051414.1651616-3-riana.tauro@intel.com


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