drm/xe/guc: Use drm_device-managed version of mutex_init()

This is safer approach and will help resolve a cleanup ordering
conflict related to the GuC ID manager.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240406143946.979-1-michal.wajdeczko@intel.com