arm: Add simple cpu_{sibling, core}_mask

arm: Add simple cpu_{sibling, core}_mask

This needs to be done for all cpus. The allocations require smp_prepare_cpus
to be called a bit later on.

In a previous version of this patch these maps were being zeroed (instead of
setting the CPU itself in them). This in turn causes cpumask_first to return
NR_CPUS, which in turn was causing default_vcpu0_location to misbehave and
read off the end of its cnt array.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Tim Deegan <tim@xen.org>
Committed-by: Ian Campbell <ian.campbell@citrix.com>