kvm, arm: Don't forward IRQ/FIQ when using the kernel's GIC

kvm, arm: Don't forward IRQ/FIQ when using the kernel's GIC

The BaseArmKvmCPU is responsible for forwarding the IRQ and FIQ
signals from gem5's simulated GIC to KVM. However, these signals
shouldn't be used when the in-kernel GIC emulator is used.

Instead of delivering the interrupts to the guest, we should just
ignore them since any such pending interrupts are likely to be an
artifact of CPU switching or incorrect draining.

Change-Id: I083b72639384272157f92f44a6606bdf0be7413c
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Sudhanshu Jha <sudhanshu.jha@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/3660