drm/i915/xehp: Add register for compute engine's MMIO-based TLB invalidation

Compute engines have a separate register that the driver should use to
perform MMIO-based TLB invalidation.

Note that the term "context" in this register's bspec description is
used to refer to the engine instance (in the same way "context" is used
on bspec 46167).

Bspec: 43930
Cc: Prathap Kumar Valsan <prathap.kumar.valsan@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Acked-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Prathap Kumar Valsan <prathap.kumar.valsan@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220428041926.1483683-3-matthew.d.roper@intel.com