tee: add sandbox driver

Adds a sandbox tee driver which emulates a generic TEE with the OP-TEE
AVB TA.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
[trini: Fix printf warnings in ta_avb_invoke_func, slots is uint]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/tee/optee/Kconfig b/drivers/tee/optee/Kconfig
index dbfa784..d489834 100644
--- a/drivers/tee/optee/Kconfig
+++ b/drivers/tee/optee/Kconfig
@@ -10,7 +10,7 @@
 	  handle Remote Procedure Calls (RPC) from OP-TEE needed to
 	  execute a service. For more information see: https://www.op-tee.org
 
-if OPTEE
+if OPTEE || SANDBOX
 
 menu "OP-TEE options"