[ARM] vgic: Treat host-to-guest routed irqs as edge-triggered

When we route host irq to guest irq:
1. We first take regular host interrupt in VGIC (i.e. vgic_routed_irq())
2. Next we determine the mapped guest irq in vgic_routed_irq()
3. Once we know the guest irq, we first lower the guest irq level
(to ensure previously raised guest irq is cleared) and then raise
the guest irq level (to ensure fresh interrupt is triggered)

Now if we treat host-to-guest irq as level-triggered then above
describe process will not work because __vgic_sync_vcpu_hwstate()
will again mark it pending before next host interrupt. To avoid
this situation we treat host-to-guest irq as edge-triggered so
that __vgic_sync_vcpu_hwstate() will not mark it pending.

Th above also apply to generic timer interrupts hence we also
treat all PPIs as edge-triggered.

Signed-off-by: Anup Patel <anup@brainfault.org>