dm: test: Add a test for the system controller uclass

Add a test to confirm that we can access system controllers and find their
driver data.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index 629de25..5218b91 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -29,6 +29,7 @@
 obj-$(CONFIG_SMSC_LPC47M) += smsc_lpc47m.o
 obj-$(CONFIG_STATUS_LED) += status_led.o
 obj-$(CONFIG_SANDBOX) += swap_case.o
+obj-$(CONFIG_SANDBOX) += syscon_sandbox.o
 obj-$(CONFIG_TWL4030_LED) += twl4030_led.o
 obj-$(CONFIG_FSL_IFC) += fsl_ifc.o
 obj-$(CONFIG_FSL_SEC_MON) += fsl_sec_mon.o