examples/vm_power: allow managing idle cores

examples/vm_power: allow managing idle cores

This change is required to allow the branch ratio algorithm to
power manage cores with no workload running on them. This is
useful both when idle cores don't use C-states and for a number of
hyperthreading scenarios.

Signed-off-by: Rory Sexton <rory.sexton@intel.com>
Reviewed-by: David Hunt <david.hunt@intel.com>
Acked-by: Reshma Pattan <reshma.pattan@intel.com>