drm/xe: add lockdep annotation for xe_device_mem_access_get()

The atomics here might hide potential issues, also rpm core is not
holding any lock when calling our rpm resume callback, so add a dummy lock
with the idea that xe_pm_runtime_resume() is eventually going to be
called when we are holding it. This only needs to happen once and then
lockdep can validate all callers and their locks.

v2: (Thomas Hellström)
 - Prefer static lockdep_map instead of full blown mutex.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Acked-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>