tee: tstee: Add Trusted Services TEE driver

The Trusted Services project provides a framework for developing and
deploying device Root of Trust services in FF-A Secure Partitions. The
FF-A SPs are accessible through the FF-A driver, but this doesn't
provide a user space interface. The goal of this TEE driver is to make
Trusted Services SPs accessible for user space clients.

All TS SPs have the same FF-A UUID, it identifies the RPC protocol used
by TS. A TS SP can host one or more services, a service is identified by
its service UUID. The same type of service cannot be present twice in
the same SP. During SP boot each service in an SP is assigned an
interface ID, this is just a short ID to simplify message addressing.
There is 1:1 mapping between TS SPs and TEE devices, i.e. a separate TEE
device is registered for each TS SP. This is required since contrary to
the generic TEE design where memory is shared with the whole TEE
implementation, in case of FF-A, memory is shared with a specific SP. A
user space client has to be able to separately share memory with each SP
based on its endpoint ID.

Acked-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Balint Dobszay <balint.dobszay@arm.com>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>