TEE driver for Trusted Services

This introduces a TEE driver for Trusted Services [1].

Trusted Services is a TrustedFirmware.org project that provides a
framework for developing and deploying device Root of Trust services in
FF-A [2] Secure Partitions. The project hosts the reference
implementation of Arm Platform Security Architecture [3] for Arm
A-profile devices.

The FF-A Secure Partitions are accessible through the FF-A driver in
Linux. However, the FF-A driver doesn't have a user space interface so
user space clients currently cannot access Trusted Services. The goal of
this TEE driver is to bridge this gap and make Trusted Services
functionality accessible from user space.

[1] https://www.trustedfirmware.org/projects/trusted-services/
[2] https://developer.arm.com/documentation/den0077/
[3] https://www.arm.com/architecture/security-features/platform-security
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