feat(arm_fpga): add ITS autodetection

Some FPGAs come with a GIC that has an ITS block configured. Since the
ITS sits between the distributor and redistributors, we can autodetect
that, and already adjust the GICR base address.

To also make this ITS usable, add an ITS node to our base DTB, and
remove that should we not find an ITS during the scan for the
redistributor. This allows to use the same TF-A binary for FPGA images
with or without an ITS.

Change-Id: I4c0417dec7bccdbad8cbca26fa2634950fc50a66
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
4 files changed