arch-arm: Remove ISA::haveGICv3CpuIfc method

The method is really not needed as we do not implement
GICv3 in legacy mode... Therefore when we want to check if
the GICv3 cpu interface is present, we can just check for
GICv3 being present

Change-Id: I264f887392d188a515480c2e31a4a4da3e67c498
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/65173
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
4 files changed