xen: move XEN_SYSCTL_physinfo, XEN_SYSCTL_numainfo and XEN_SYSCTL_topologyinfo to...

xen: move XEN_SYSCTL_physinfo, XEN_SYSCTL_numainfo and XEN_SYSCTL_topologyinfo to common code

Move XEN_SYSCTL_physinfo, XEN_SYSCTL_numainfo and
XEN_SYSCTL_topologyinfo from x86/sysctl.c to common/sysctl.c.

The implementation of XEN_SYSCTL_physinfo is mostly generic but needs to
fill in few arch specific details: introduce arch_do_physinfo to do that.

The implementation of XEN_SYSCTL_physinfo relies on two global
variables: total_pages and cpu_khz. Make them available on ARM.

Implement node_spanned_pages and __node_distance on ARM, assuming 1 numa
node for now.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Keir Fraser <keir@xen.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>