dt/bindings: add bindings for optee

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";

		};

	};

lantiq	Lantiq Semiconductor

lenovo	Lenovo Group Ltd.

lg	LG Corporation

linaro	Linaro Limited

linux	Linux-specific binding

lsi	LSI Corp. (LSI Logic)

lltc	Linear Technology Corporation