examples/vm_power: make branch ratio threshold per core

This modification allows for the branch ratio threshold to be set
per core rather than system wide. This gives greater flexibility to
the branch ratio monitoring allowing it to manage different
workloads with different characteristics on the same system.

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>