xen/sched: introduce cpupool_update_node_affinity()

xen/sched: introduce cpupool_update_node_affinity()

For updating the node affinities of all domains in a cpupool add a new
function cpupool_update_node_affinity().

In order to avoid multiple allocations of cpumasks carve out memory
allocation and freeing from domain_update_node_affinity() into new
helpers, which can be used by cpupool_update_node_affinity().

Modify domain_update_node_affinity() to take an additional parameter
for passing the allocated memory in and to allocate and free the memory
via the new helpers in case NULL was passed.

This will help later to pre-allocate the cpumasks in order to avoid
allocations in stop-machine context.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Tested-by: Andrew Cooper <andrew.cooper3@citrix.com>