drm/xe/guc: Make creation of SLPC debugfs files conditional

drm/xe/guc: Make creation of SLPC debugfs files conditional

Platforms that do not support SLPC are exempted from the GuC PC support.
The GuC PC does not get initialized, and neither do its BOs get created.

This causes a problem because the GuC PC debugfs file is still being
created. Whenever the file is attempted to read, it causes a NULL
pointer dereference on the supposed BO of the GuC PC.

So, make the creation of SLPC debugfs files conditional to when SLPC
features are supported.

Fixes: aaab5404b16f ("drm/xe: Introduce GuC PC debugfs")
Suggested-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
Reviewed-by: Stuart Summers <stuart.summers@intel.com>
Signed-off-by: Aradhya Bhatia <aradhya.bhatia@intel.com>
Link: https://lore.kernel.org/r/20250516141902.5614-1-aradhya.bhatia@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>