dm: core: Access device flags through functions

At present flags are stored as part of the device. In preparation for
storing them separately, change the access to go through inline functions.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/cpu.c b/test/dm/cpu.c
index 28869c1..ed12caf 100644
--- a/test/dm/cpu.c
+++ b/test/dm/cpu.c
@@ -25,7 +25,7 @@
 	for (uclass_find_first_device(UCLASS_CPU, &dev);
 	     dev;
 	     uclass_find_next_device(&dev))
-		ut_assert(dev->flags & DM_FLAG_ACTIVATED);
+		ut_assert(dev_get_flags(dev) & DM_FLAG_ACTIVATED);
 
 	ut_assertok(uclass_get_device_by_name(UCLASS_CPU, "cpu-test1", &dev));
 	ut_asserteq_ptr(cpu_get_current_dev(), dev);