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/arch/sandbox/dts/test.dts b/arch/sandbox/dts/test.dts
index 5752bf5..01e6bc0 100644
--- a/arch/sandbox/dts/test.dts
+++ b/arch/sandbox/dts/test.dts
@@ -382,6 +382,10 @@
 		remoteproc-name = "remoteproc-test-dev2";
 	};
 
+	smem@0 {
+		compatible = "sandbox,smem";
+	};
+
 	spi@0 {
 		#address-cells = <1>;
 		#size-cells = <0>;