dm: eth: Add basic driver model support to Ethernet stack

First just add support for MAC drivers.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/README.drivers.eth b/doc/README.drivers.eth
index 42af442..8b4d352 100644
--- a/doc/README.drivers.eth
+++ b/doc/README.drivers.eth
@@ -1,3 +1,9 @@
+!!! WARNING !!!
+
+This guide describes to the old way of doing things. No new Ethernet drivers
+should be implemented this way. All new drivers should be written against the
+U-Boot core driver model. See doc/driver-model/README.txt
+
 -----------------------
  Ethernet Driver Guide
 -----------------------