hw/intc/arm_gicv3_its: Implement state save/restore

hw/intc/arm_gicv3_its: Implement state save/restore

We need to handle both registers and ITS tables. While
register handling is standard, ITS table handling is more
challenging since the kernel API is devised so that the
tables are flushed into guest RAM and not in vmstate buffers.

Flushing the ITS tables on device pre_save() is too late
since the guest RAM is already saved at this point.

Table flushing needs to happen when we are sure the vcpus
are stopped and before the last dirty page saving. The
right point is RUN_STATE_FINISH_MIGRATE but sometimes the
VM gets stopped before migration launch so let's simply
flush the tables each time the VM gets stopped.

For regular ITS registers we just can use vmstate pre_save()
and post_load() callbacks.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Message-id: 1497023553-18411-3-git-send-email-eric.auger@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>