vmstate: Add support for two dimensional arrays

Add support for migrating two dimensional arrays, by defining
a set of new macros VMSTATE_*_2DARRAY paralleling the existing
VMSTATE_*_ARRAY macros. 2D arrays are handled the same for actual
state serialization; the only difference is that the type check
has to change for a 2D array.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Igor Mitsyanko <i.mitsyanko@gmail.com>
Message-id: 1363975375-3166-2-git-send-email-peter.maydell@linaro.org
