arch/optee: Add OPTEE architecture

Add a new architecture to support the OP-TEE execution environment

The SCP Firmware will run as a Pseudo Trusted Application (PTA) in
OP-TEE thread context.

OP-TEE invoke method will be used to send request to the SCMI server.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>