drm/xe: Introduce const cast helper

Typically we want to preserve pointer constness when converting
from one xe pointer to another, but in some rare cases, like kunit
parameter conversions, we might want to discard this constness.
Add a helper that we will use to clearly indicate our intention.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com> #v1
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240720142528.530-2-michal.wajdeczko@intel.com

drivers/gpu/drm/xe/xe_device.h

@@ -20,6 +20,11 @@ static inline struct xe_device *pdev_to_xe_device(struct pci_dev *pdev)
 	return pci_get_drvdata(pdev);
 }
 
+static inline struct xe_device *xe_device_const_cast(const struct xe_device *xe)
+{
+	return (struct xe_device *)xe;
+}
+
 static inline struct xe_device *ttm_to_xe_device(struct ttm_device *ttm)
 {
 	return container_of(ttm, struct xe_device, ttm);