KVM: arm64: vgic-its: Introduce migration ABI infrastructure

We plan to support different migration ABIs, ie. characterizing
the ITS table layout format in guest RAM. For example, a new ABI
will be needed if vLPIs get supported for nested use case.

So let's introduce an array of supported ABIs (at the moment a single
ABI is supported though). The following characteristics are foreseen
to vary with the ABI: size of table entries, save/restore operation,
the way abi settings are applied.

By default the MAX_ABI_REV is applied on its creation. In subsequent
patches we will introduce a way for the userspace to change the ABI
in use.

The entry sizes now are set according to the ABI version and not
hardcoded anymore.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Christoffer Dall <cdall@linaro.org>

include/kvm/arm_vgic.h

@@ -162,6 +162,9 @@ struct vgic_its {
 	u32			creadr;
 	u32			cwriter;
 
+	/* migration ABI revision in use */
+	u32			abi_rev;
+
 	/* Protects the device and collection lists */
 	struct mutex		its_lock;
 	struct list_head	device_list;