drm/i915/guc: Remove GuC stage descriptor, add LRC descriptor

Remove old GuC stage descriptor, add LRC descriptor which will be used
by the new GuC interface implemented in this patch series.

v2:
 (John Harrison)
  - s/lrc/LRC/g

Cc: John Harrison <john.c.harrison@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210721215101.139794-3-matthew.brost@intel.com