drm/xe: Allow const propagation in gt_to_xe()

Replace the inline function with a _Generic() so gt_to_xe() can work
with a const struct xe_gt*, which leads to a const struct xe *.
This allows a const gt being passed around and when the xe device is
needed, compiler won't issue a warning that calling gt_to_xe() would
discard the const. Rather, just propagate the const to the xe pointer
being returned.
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_gt.h

@@ -49,10 +49,10 @@ static inline bool xe_gt_is_media_type(struct xe_gt *gt)
 	return gt->info.type == XE_GT_TYPE_MEDIA;
 }
 
-static inline struct xe_device * gt_to_xe(struct xe_gt *gt)
-{
-	return gt->xe;
-}
+#define gt_to_xe(gt__)								\
+	_Generic(gt__,								\
+		 const struct xe_gt *: (const struct xe_device *)((gt__)->xe),	\
+		 struct xe_gt *: (gt__)->xe)
 
 static inline bool xe_gt_is_usm_hwe(struct xe_gt *gt, struct xe_hw_engine *hwe)
 {