dev-arm: Make GICv3 maintenance interrupt an ArmInterrupt

Change-Id: I88e2b72849cdf3f69026c62517303837e7d3d551
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Anouk Van Laer <anouk.vanlaer@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17629
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>