Update the GIC save/restore to use vmstate rather than hand-rolled
save/load functions.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Igor Mitsyanko <i.mitsyanko@gmail.com>
Message-id: 1363975375-3166-4-git-send-email-peter.maydell@linaro.org