xen/sched: use sched_resource cpu instead smp_processor_id in schedulers

xen/sched: use sched_resource cpu instead smp_processor_id in schedulers

Especially in the do_schedule() functions of the different schedulers
using smp_processor_id() for the local cpu number is correct only if
the sched_unit is a single vcpu. As soon as larger sched_units are
used most uses should be replaced by the master_cpu number of the local
sched_resource instead.

Add a helper to get that sched_resource master_cpu and modify the
schedulers to use it in a correct way.

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