common: Drop bootstage.h from common header

Move this fairly uncommon header out of the common header.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/net/eth_legacy.c b/net/eth_legacy.c
index 5d6b0d7..e0ef4a1 100644
--- a/net/eth_legacy.c
+++ b/net/eth_legacy.c
@@ -6,6 +6,7 @@
  */
 
 #include <common.h>
+#include <bootstage.h>
 #include <command.h>
 #include <env.h>
 #include <net.h>