xen/arm: physical irq follow virtual irq

xen/arm: physical irq follow virtual irq

Migrate physical irqs to the same physical cpu that is running the vcpu
expected to receive the irqs. That is done when enabling irqs, when the
guest writes to GICD_ITARGETSR and when Xen migrates a vcpu to a
different pcpu.

In case of virq migration, if the virq is inflight and in a GICH_LR
register already, delay migrating the corresponding physical irq until
the virq is EOIed by the guest and the MIGRATING flag has been cleared.
This way we make sure that the pcpu running the old vcpu gets
interrupted with a new irq of the same kind, clearing the GICH_LR sooner.

Introduce a new arch specific function, arch_move_irqs, that is empty on
x86 and implements the vgic irq migration code on ARM.
arch_move_irqs is going to be called by from sched.c.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Julien Grall <julien.grall@linaro.org>