x86: allow specifying the NUMA nodes Dom0 should run on

x86: allow specifying the NUMA nodes Dom0 should run on

... by introducing a "dom0_nodes" option augmenting the "dom0_mem" and
"dom0_max_vcpus" ones.

Note that this gives meaning to MEMF_exact_node specified alone (i.e.
implicitly combined with NUMA_NO_NODE): In such a case any node inside
the domain's node mask is acceptable, but no other node. This changed
behavior is (implicitly) being exposed through the memop hypercalls.

Note further that this change doesn't take care of moving the initrd
image into memory matching Dom0's affinity when the initrd doesn't get
copied (because of being part of the initial mapping) anyway.

And note finally that this doesn't get us meaningfully closer to
handing vNUMA information to Dom0 (which will require the current
striping of allocations to become node-specific in order for the passed
on information to be meaningful).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: Dario Faggioli <dario.faggioli@cirix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>