dm: test: Add a test for the ram uclass

Add a test to confirm that we can probe this device and get information on
the available RAM.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/ram/Makefile b/drivers/ram/Makefile
index 4494d81..0e10249 100644
--- a/drivers/ram/Makefile
+++ b/drivers/ram/Makefile
@@ -5,3 +5,4 @@
 # SPDX-License-Identifier:      GPL-2.0+
 #
 obj-$(CONFIG_RAM) += ram-uclass.o
+obj-$(CONFIG_SANDBOX) += sandbox_ram.o