ppc/spapr-caps: Change migration macro to take full spapr-cap name

ppc/spapr-caps: Change migration macro to take full spapr-cap name

Change the macro that generates the vmstate migration field and the needed
function for the spapr-caps to take the full spapr-cap name. This has
the benefit of meaning this instance will be picked up when greping
for the spapr-caps and making it more obvious what this macro is doing.

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>