drm/xe/pvc: Blacklist BCS_SWCTRL register

Wa_16017236439 requires the BCS_SWCTRL to be privileged.

v2: Define and use BCS_SWCTRL()

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>