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/include/dm/uclass-id.h b/include/dm/uclass-id.h
index 047ac15..84a6955 100644
--- a/include/dm/uclass-id.h
+++ b/include/dm/uclass-id.h
@@ -38,6 +38,7 @@
 	UCLASS_PCI,		/* PCI bus */
 	UCLASS_PCI_GENERIC,	/* Generic PCI bus device */
 	UCLASS_PCH,		/* x86 platform controller hub */
+	UCLASS_ETH,		/* Ethernet device */
 
 	UCLASS_COUNT,
 	UCLASS_INVALID = -1,