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/configs/sandbox_defconfig b/configs/sandbox_defconfig
index 2fc84a1..47f6bfd 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -200,3 +200,5 @@
 CONFIG_UT_DM=y
 CONFIG_UT_ENV=y
 CONFIG_UT_OVERLAY=y
+CONFIG_SMEM=y
+CONFIG_SANDBOX_SMEM=y