xen/sched: support differing granularity in schedule_cpu_[add/rm]()

xen/sched: support differing granularity in schedule_cpu_[add/rm]()

With core scheduling active schedule_cpu_[add/rm]() has to cope with
different scheduling granularity: a cpu not in any cpupool is subject
to granularity 1 (cpu scheduling), while a cpu in a cpupool might be
in a scheduling resource with more than one cpu.

Handle that by having arrays of old/new pdata and vdata and loop over
those where appropriate.

Additionally the scheduling resource(s) must either be merged or
split.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Dario Faggioli <dfaggioli@suse.com>