cuda: embed mos6522_cuda device directly rather than using QOM object link

cuda: embed mos6522_cuda device directly rather than using QOM object link

Examining the migration stream it can be seen that the mos6522 device state is
being stored separately rather than as part of the CUDA device which is
incorrect (and likely to cause issues if another mos6522 device is added to
the machine).

Resolve this by embedding the mos6522_cuda device directly within the CUDA
device rather than using a QOM object link to reference the device separately.

Note that we also bump the version in vmstate_cuda to reflect this change: this
isn't particularly important for the moment as the Mac machine migration isn't
100% reliable due to issues migrating the timebase under TCG.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>