Previously, the effective values of the various spapr capability flags
were only determined at machine reset time.  That was a lazy way of making
sure it was after cpu initialization so it could use the cpu object to
inform the defaults.

But we've now improved the compat checking code so that we don't need to
instantiate the cpus to use it.  That lets us move the resolution of the
capability defaults much earlier.

This is going to be necessary for some future capabilities.
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>
Reviewed-by: NGreg Kurz <groug@kaod.org>
Reviewed-by: NCédric Le Goater <clg@kaod.org>