hw/intc/arm_gicv3_its: Revert version increments in vmstate_its

hw/intc/arm_gicv3_its: Revert version increments in vmstate_its

Commit 18f6290a6a ("hw/intc: GICv3 ITS initial framework")
incremented version_id and minimum_version_id fields of
VMStateDescription vmstate_its. This breaks the migration between
6.2 and 6.1 with the following message:

qemu-system-aarch64: savevm: unsupported version 1 for 'arm_gicv3_its' v0
qemu-system-aarch64: load of migration failed: Invalid argument

Revert that change.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Message-id: 20211122171020.1195483-1-eric.auger@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>