drm/i915: Don't force serialisation on marking up execlists irq posted

Since we coordinate with the execlists tasklet using a locked schedule
operation that ensures that after we set the engine->irq_posted we
always have an invocation of the tasklet, we do not need to use a locked
operation to set the engine->irq_posted itself.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170517121007.27224-12-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_irq.c

@@ -1360,7 +1360,7 @@ gen8_cs_irq_handler(struct intel_engine_cs *engine, u32 iir, int test_shift)
 
 	if (iir & (GT_CONTEXT_SWITCH_INTERRUPT << test_shift)) {
 		if (port_count(&engine->execlist_port[0])) {
-			set_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
+			__set_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
 			tasklet = true;
 		}
 	}