drm/xe: Normalize default param values

drm/xe: Normalize default param values

Document xe module params with the default values following a similar
strategy for all of them:

	1) Define a DEFAULT_* macro with the default value. When the
	   value can't be directly stringified, also define a *_STR
	   variant
	2) Use __stringify() or the _STR variant to make sure the
	   default value shows up in the param description

This allows us to show the correct default according to the
configuration. max_vfs for example was wrongly documented for
CONFIG_DRM_XE_DEBUG and svm_notifier_size didn't have its default
documented.

Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://lore.kernel.org/r/20250626-guc-log-level-v3-1-c3ed8b452e91@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>