arm64: Include support for FF-A

Arm released the first version of the Arm Firmware Framework for Arm A-profile[1] (FF-A) in 2020. The framework provides, among other, a generic transport protocol for communication between components at different execution levels (EL) in the Arm-A architecture, including between the secure execution environment and the normal execution environment.

FF-A support exists in the Linux kernel, in OP-TEE and in Xen (tech preview). This makes FF-A a viable and more modern approach for Apertis when using OP-TEE and optionally Xen on an Arm-A platform. In this context, FF-A replaces the OP-TEE specific transport protocol and instead provides a more generic solution not tied to OP-TEE.

[1] https://developer.arm.com/documentation/den0077/latest/

Signed-off-by: Boris Klintefjord fixed-term.Boris.Klintefjord@se.bosch.com