drm/xe: Use ordered WQ for G2H handler

System work queues are shared, use a dedicated work queue for G2H
processing to avoid G2H processing getting block behind system tasks.

Fixes: dd08ebf6

 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Cc: <stable@vger.kernel.org>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Francois Dugast <francois.dugast@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240506034758.3697397-1-matthew.brost@intel.com