Add vmstate support for migrating arrays of CPU_DoubleU via
VMSTATE_CPUDOUBLE_ARRAY.

Signed-off-by: Juan Quintela <quintela@redhat.com>
[PMM: rebased, since files have all moved since 2012;
 added VMSTATE_CPUDOUBLE_ARRAY_V for consistency with FLOAT64]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>