drm/xe/ggtt: Use scope-based runtime pm
Switch the GGTT code to scope-based runtime PM for consistency with
other parts of the driver.
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://patch.msgid.link/20251118164338.3572146-51-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>