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/Makefile b/drivers/tee/Makefile
index 19633b6..f72c68c 100644
--- a/drivers/tee/Makefile
+++ b/drivers/tee/Makefile
@@ -1,4 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0+
 
 obj-y += tee-uclass.o
+obj-$(CONFIG_SANDBOX) += sandbox.o
 obj-$(CONFIG_OPTEE) += optee/