Cycles: oneAPI: add support for SYCL host task

This functionality is related only to debugging of SYCL implementation
via single-threaded CPU execution and is disabled by default.
Host device has been deprecated in SYCL 2020 spec and we removed it
in 305b92e05f.
Since this is still very useful for debugging, we're restoring a
similar functionality here through SYCL 2020 Host Task.

intern/cycles/kernel/device/oneapi/kernel.cpp

@@ -230,6 +230,12 @@ bool oneapi_enqueue_kernel(KernelContext *kernel_context,
     /* NOTE(@nsirgien): As for now non-uniform work-groups don't work on most oneAPI devices,
      * we extend work size to fit uniformity requirements. */
     global_size = groups_count * local_size;
+
+#  ifdef WITH_ONEAPI_SYCL_HOST_TASK
+    /* Path array implementation is serial in case of SYCL Host Task execution. */
+    global_size = 1;
+    local_size = 1;
+#  endif
   }
 
   /* Let the compiler throw an error if there are any kernels missing in this implementation. */