drm/xe/doc: Include documentation about xe_assert()

Our xe_assert() macros are well documented.
Include that in master documentation.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20231115112921.1905-1-michal.wajdeczko@intel.com


Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>