drm/i915: Disable preempt busywait when using GuC scheduling

Disable preempt busywait when using GuC scheduling. This isn't needed as
the GuC controls preemption when scheduling.

v2:
 (John H):
  - Fix commit message

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/20210721215101.139794-12-matthew.brost@intel.com

drivers/gpu/drm/i915/gt/gen8_engine_cs.c

@@ -506,7 +506,8 @@ gen8_emit_fini_breadcrumb_tail(struct i915_request *rq, u32 *cs)
 	*cs++ = MI_USER_INTERRUPT;
 
 	*cs++ = MI_ARB_ON_OFF | MI_ARB_ENABLE;
-	if (intel_engine_has_semaphores(rq->engine))
+	if (intel_engine_has_semaphores(rq->engine) &&
+	    !intel_uc_uses_guc_submission(&rq->engine->gt->uc))
 		cs = emit_preempt_busywait(rq, cs);
 
 	rq->tail = intel_ring_offset(rq, cs);
@@ -598,7 +599,8 @@ gen12_emit_fini_breadcrumb_tail(struct i915_request *rq, u32 *cs)
 	*cs++ = MI_USER_INTERRUPT;
 
 	*cs++ = MI_ARB_ON_OFF | MI_ARB_ENABLE;
-	if (intel_engine_has_semaphores(rq->engine))
+	if (intel_engine_has_semaphores(rq->engine) &&
+	    !intel_uc_uses_guc_submission(&rq->engine->gt->uc))
 		cs = gen12_emit_preempt_busywait(rq, cs);
 
 	rq->tail = intel_ring_offset(rq, cs);