irqchip/GICv3: Don't deactivate interrupts forwarded to a guest

Commit 0a4377de

 ("genirq: Introduce irq_set_vcpu_affinity() to
target an interrupt to a VCPU") added just what we needed at the
lowest level to allow an interrupt to be deactivated by a guest.

When such a request reaches the GIC, it knows it doesn't need to
perform the deactivation anymore, and can safely leave the guest
do its magic. This of course requires additional support in both
VFIO and KVM.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-and-tested-by: Eric Auger <eric.auger@linaro.org>
Cc: Christoffer Dall <christoffer.dall@linaro.org>
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Cc: <linux-arm-kernel@lists.infradead.org>
Cc: kvmarm@lists.cs.columbia.edu
Cc: Jason Cooper <jason@lakedaemon.net>
Link: http://lkml.kernel.org/r/1440604845-28229-3-git-send-email-marc.zyngier@arm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>