hvmloader: limit CPUs exposed to guests

hvmloader: limit CPUs exposed to guests

Various Linux versions allocate (partial) per-CPU data for all of them,
as there is no indication in MADT whether they're hotpluggable. That's
a little wasteful in terms of resource consumption especially for
- guests with not overly much memory assigned,
- 32-bit guests not having overly much address space available.
Therefore limit what we put into MADT to the "maxvcpus" value, and make
sure AML doesn't touch memory addresses corresponding to CPUs beyond
that value (we can't reasonably make the respective processor objects
disappear).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>