dm: core: Add support for simple-bus

Add a driver for the simple-bus nodes, which allows devices within these
nodes to be bound.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/Makefile b/drivers/core/Makefile
index c7905b1..151c239 100644
--- a/drivers/core/Makefile
+++ b/drivers/core/Makefile
@@ -5,3 +5,4 @@
 #
 
 obj-y := device.o lists.o root.o uclass.o util.o
+obj-$(CONFIG_OF_CONTROL) += simple-bus.o