feat(rpi): add Raspberry Pi 5 support

The Raspberry Pi 5 is a single-board computer based on BCM2712 that
contains four Arm Cortex-A76 cores.

This change introduces minimal BL31 support with PSCI that has been
validated to boot Linux and a private EDK2 build.

It's a drop-in replacement for the custom TF-A armstub now included in
the EEPROM images.

Change-Id: Id72a0370f54e71ac97c3daa1bacedacb7dec148f
Signed-off-by: Mario Bălănică <mariobalanica02@gmail.com>
8 files changed