drivers: smem: sandbox

Add Sandbox driver for SMEM. mostly stub operations.

Signed-off-by: Ramon Fried <ramon.fried@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/smem/Makefile b/drivers/smem/Makefile
index 605b8fc..af3e9b5 100644
--- a/drivers/smem/Makefile
+++ b/drivers/smem/Makefile
@@ -2,5 +2,6 @@
 #
 # Makefile for the U-Boot SMEM interface drivers
 
+obj-$(CONFIG_SANDBOX_SMEM) += sandbox_smem.o
 obj-$(CONFIG_SMEM) += smem-uclass.o
 obj-$(CONFIG_MSM_SMEM) += msm_smem.o