dt/bindings: add bindings for optee

Sync with c8bfafb15944 ("dt/bindings: add bindings for optee")
from Linux kernel.

Introduces linaro prefix and adds bindings for ARM TrustZone based OP-TEE
implementation.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>

doc/device-tree-bindings/firmware/linaro,optee-tz.txt

@@ -0,0 +1,31 @@
+OP-TEE Device Tree Bindings
+
+OP-TEE is a piece of software using hardware features to provide a Trusted
+Execution Environment. The security can be provided with ARM TrustZone, but
+also by virtualization or a separate chip.
+
+We're using "linaro" as the first part of the compatible property for
+the reference implementation maintained by Linaro.
+
+* OP-TEE based on ARM TrustZone required properties:
+
+- compatible     : should contain "linaro,optee-tz"
+
+- method         : The method of calling the OP-TEE Trusted OS. Permitted
+                   values are:
+
+                   "smc" : SMC #0, with the register assignments specified
+		           in drivers/tee/optee/optee_smc.h
+
+                   "hvc" : HVC #0, with the register assignments specified
+		           in drivers/tee/optee/optee_smc.h
+
+
+
+Example:
+	firmware {
+		optee {
+			compatible = "linaro,optee-tz";
+			method = "smc";
+		};
+	};