sandbox: add sandbox sm uclass driver

This patch adds sandbox secure monitor driver.

Signed-off-by: Alexey Romanov <avromanov@salutedevices.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Link: https://lore.kernel.org/r/20230921081346.22157-3-avromanov@salutedevices.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
diff --git a/drivers/sm/Makefile b/drivers/sm/Makefile
index 9f4683b..af5f475 100644
--- a/drivers/sm/Makefile
+++ b/drivers/sm/Makefile
@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0-only
 
 obj-y += sm-uclass.o
+obj-$(CONFIG_SANDBOX) += sandbox-sm.o