dm: Add a demonstration/example driver

As an example of how to write a uclass and a driver, provide a demo version
of each, accessible through the 'demo' command.

To use these with driver model, define CONFIG_CMD_DEMO and CONFIG_DM_DEMO.

The two demo drivers are enabled with CONFIG_DM_DEMO_SIMPLE and
CONFIG_DM_DEMO_SHAPE.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Pavel Herrmann <morpheus.ibis@gmail.com>
Signed-off-by: Viktor Křivák <viktor.krivak@gmail.com>
Signed-off-by: Tomas Hlavacek <tmshlvck@gmail.com>
diff --git a/include/configs/sandbox.h b/include/configs/sandbox.h
index 8e034a7..1d11c40 100644
--- a/include/configs/sandbox.h
+++ b/include/configs/sandbox.h
@@ -21,7 +21,11 @@
 #define CONFIG_BOOTSTAGE
 #define CONFIG_BOOTSTAGE_REPORT
 #define CONFIG_DM
+#define CONFIG_CMD_DEMO
 #define CONFIG_CMD_DM
+#define CONFIG_DM_DEMO
+#define CONFIG_DM_DEMO_SIMPLE
+#define CONFIG_DM_DEMO_SHAPE
 #define CONFIG_DM_TEST
 
 /* Number of bits in a C 'long' on this architecture */