dev-arm: Use FdtState to generate GIC properites

dev-arm: Use FdtState to generate GIC properites

Rather than hardcoding property values, we use a FdtState variable, so
that it is possible to retrieve them from an external object.

Change-Id: Ifd90814b03c68a7f55ef3be6123dcfee5e1de568
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20051
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>