xen/arm: run the vtimer Xen timers on the pcpu the vcpu is running on

xen/arm: run the vtimer Xen timers on the pcpu the vcpu is running on

The Xen physical timer emulator and virtual timer driver use two
internal Xen timers: initialize them on the pcpu the vcpu is running on,
rather than the processor that it's creating the vcpu.

On vcpu restore migrate the phys_timer and the virt_timer to the
pcpu the vcpu is running on.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>