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/include/dm/uclass-id.h b/include/dm/uclass-id.h
index 0ea7a6f..a8944c9 100644
--- a/include/dm/uclass-id.h
+++ b/include/dm/uclass-id.h
@@ -19,6 +19,7 @@
 	UCLASS_TEST_FDT,
 	UCLASS_TEST_BUS,
 	UCLASS_SPI_EMUL,	/* sandbox SPI device emulator */
+	UCLASS_SIMPLE_BUS,
 
 	/* U-Boot uclasses start here */
 	UCLASS_GPIO,		/* Bank of general-purpose I/O pins */