dm: add DM_FLAG_BOUND flag

Currently, we only have DM_FLAG_ACTIVATED to indicate the device
status, but we still cannot know in which stage is in progress,
binding or probing.

This commit introduces a new flag, DM_FLAG_BOUND, which is set when
the device is really bound, and cleared when it is unbound.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/include/dm/device.h b/include/dm/device.h
index 12fd02d..4cd7ba3 100644
--- a/include/dm/device.h
+++ b/include/dm/device.h
@@ -36,6 +36,9 @@
 /* Allocate driver private data on a DMA boundary */
 #define DM_FLAG_ALLOC_PRIV_DMA	(1 << 5)
 
+/* Device is bound */
+#define DM_FLAG_BOUND	(1 << 6)
+
 /**
  * struct udevice - An instance of a driver
  *