kernel: object: rename z_object_init to k_object_init

Do not use z_ for internal API and rename to k_object_init.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/kernel/device.c b/kernel/device.c
index d5ceb61..8a07e4a 100644
--- a/kernel/device.c
+++ b/kernel/device.c
@@ -21,7 +21,7 @@
 void z_device_state_init(void)
 {
 	STRUCT_SECTION_FOREACH(device, dev) {
-		z_object_init(dev);
+		k_object_init(dev);
 	}
 }