Add UCLASS_TEE for Trusted Execution Environment

Adds a uclass to interface with a TEE (Trusted Execution Environment).

A TEE driver is a driver that interfaces with a trusted OS running in
some secure environment, for example, TrustZone on ARM cpus, or a
separate secure co-processor etc.

The TEE subsystem can serve a TEE driver for a Global Platform compliant
TEE, but it's not limited to only Global Platform TEEs.

The over all design is based on the TEE subsystem in the Linux kernel,
tailored for U-Boot.

Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Igor Opaniuk <igor.opaniuk@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/drivers/tee/Kconfig b/drivers/tee/Kconfig
new file mode 100644
index 0000000..f3fc3c2
--- /dev/null
+++ b/drivers/tee/Kconfig
@@ -0,0 +1,11 @@
+# Generic Trusted Execution Environment Configuration
+config TEE
+	bool "Trusted Execution Environment support"
+	depends on ARM && (ARM64 || CPU_V7A)
+	select ARM_SMCCC
+	help
+	  This implements a generic interface towards a Trusted Execution
+	  Environment (TEE). A TEE is a trusted OS running in some secure
+	  environment, for example, TrustZone on ARM cpus, or a separate
+	  secure co-processor etc. See also:
+	  https://en.wikipedia.org/wiki/Trusted_execution_environment