Merge branch '2023-07-24-introduce-FF-A-suppport'

To quote the author:
Adding support for Arm FF-A v1.0 (Arm Firmware Framework for Armv8-A) [A].

FF-A specifies interfaces that enable a pair of software execution
environments aka partitions to communicate with each other. A partition
could be a VM in the Normal or Secure world, an application in S-EL0, or
a Trusted OS in S-EL1.

FF-A is a discoverable bus and similar to architecture features.
FF-A bus is discovered using ARM_SMCCC_FEATURES mechanism performed
by the PSCI driver.

   => dm tree

    Class     Index  Probed  Driver                Name
   -----------------------------------------------------------
   ...
    firmware      0  [ + ]   psci                      |-- psci
    ffa                   0  [   ]   arm_ffa               |   `-- arm_ffa
   ...

Clients are able to probe then use the FF-A bus by calling the DM class
searching APIs (e.g: uclass_first_device).

This implementation of the specification provides support for Aarch64.

The FF-A driver uses the SMC ABIs defined by the FF-A specification to:

    - Discover the presence of secure partitions (SPs) of interest
    - Access an SP's service through communication protocols
      (e.g: EFI MM communication protocol)

The FF-A support provides the following features:

    - Being generic by design and can be used by any Arm 64-bit platform
    - FF-A support can be compiled and used without EFI
    - Support for SMCCCv1.2 x0-x17 registers
    - Support for SMC32 calling convention
    - Support for 32-bit and 64-bit FF-A direct messaging
    - Support for FF-A MM communication (compatible with EFI boot time)
    - Enabling FF-A and MM communication in Corstone1000 platform as a use case
    - A Uclass driver providing generic FF-A methods.
    - An Arm FF-A device driver providing Arm-specific methods and
      reusing the Uclass methods.
    - A sandbox emulator for Arm FF-A, emulates the FF-A side of the
      Secure World and provides FF-A ABIs inspection methods.
    - An FF-A sandbox device driver for FF-A communication with the
      emulated Secure World.  The driver leverages the FF-A Uclass to
      establish FF-A communication.
    - Sandbox FF-A test cases.
    - A new command called armffa is provided as an example of how to
      access the FF-A bus

For more details about the FF-A support please refer to [B] and refer to [C] for
how to use the armffa command.

Please find at [D] an example of the expected boot logs when enabling
FF-A support for a platform. In this example the platform is
Corstone1000. But it can be any Arm 64-bit platform.

[A]: https://developer.arm.com/documentation/den0077/latest/
[B]: doc/arch/arm64.ffa.rst
[C]: doc/usage/cmd/armffa.rst
[D]: example of boot logs when enabling FF-A