[SYCL] Make Level-Zero events visible on the host (#2576)

The runtime is waiting for many of them there.

Signed-off-by: Sergey V Maslov <sergey.v.maslov@intel.com>

Author: smaslov-intel

sycl/plugins/level_zero/pi_level_zero.cpp

@@ -228,7 +228,13 @@ _pi_context::getFreeSlotInExistingOrNewPool(ze_event_pool_handle_t &ZePool,
     ze_event_pool_desc_t ZeEventPoolDesc = {};
     ZeEventPoolDesc.stype = ZE_STRUCTURE_TYPE_EVENT_POOL_DESC;
     ZeEventPoolDesc.count = MaxNumEventsPerPool;
-    ZeEventPoolDesc.flags = ZE_EVENT_POOL_FLAG_KERNEL_TIMESTAMP;
+
+    // Make all events visible on the host.
+    // TODO: events that are used only on device side APIs can be optimized
+    // to not be from the host-visible pool.
+    //
+    ZeEventPoolDesc.flags =
+        ZE_EVENT_POOL_FLAG_HOST_VISIBLE | ZE_EVENT_POOL_FLAG_KERNEL_TIMESTAMP;
 
     std::vector<ze_device_handle_t> ZeDevices;
     std::for_each(Devices.begin(), Devices.end(),