drm/xe: make xe_gt_idle_disable_c6() handle the forcewake internally

Move forcewake_get() into xe_gt_idle_enable_c6() to streamline the
code and make it easier to use.

Suggested-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Xin Wang <x.wang@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://lore.kernel.org/r/20250827000633.1369890-2-x.wang@intel.com


Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>