Introduce new attributes in KVM_DEV_ARM_VGIC_GRP_CTRL group:
- KVM_DEV_ARM_ITS_SAVE_TABLES: saves the ITS tables into guest RAM
- KVM_DEV_ARM_ITS_RESTORE_TABLES: restores them into VGIC internal
  structures.

We hold the vcpus lock during the save and restore to make
sure no vcpu is running.

At this stage the functionality is not yet implemented. Only
the skeleton is put in place.
Signed-off-by: NEric Auger <eric.auger@redhat.com>
[Given we will move the iodev register until setting the base addr]
Reviewed-by: NChristoffer Dall <cdall@linaro.org>