drm/xe: Avoid any races around ccs_mode update

Ensure that there are no drm clients when changing CCS mode.
Allow exec_queue creation only with enabled CCS engines.

v2: Rebase

Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>