xen/gic: EOI irqs on the right pcpu

xen/gic: EOI irqs on the right pcpu

We need to write the irq number to GICC_DIR on the physical cpu that
previously received the interrupt, but currently we are doing it on the
pcpu that received the maintenance interrupt. As a consequence if a
vcpu is migrated to a different pcpu, the irq is going to be EOI'ed on
the wrong pcpu.

This covers the case where dom0 vcpu0 is running on pcpu1 for example
(you can test this scenario by using xl vcpu-pin).

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>