feat(gicv3): multichip: detect GIC-700 at runtime

At the moment we have a GIC_ENABLE_V4_EXTN build time variable to
determine whether the GIC interrupt controller is compliant to version
4.0 of the GIC spec or not.
In case of the GIC-600 multichip support we were somewhat abusing that
flag to differentiate between a GIC-700 and GIC-600 implementation
being used in the system.

To avoid a build time dependency on this flag, look at the GICD_IIDR
register and check if the hardware is a GIC-600 or not, to make this
decision at runtime. We then use the values for either GIC-700 or the
GIC-600, respectively.

Change-Id: I8c09ec1cd6fd60d28da879ed55ffef5506f9869d
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
2 files changed