examples/power: change 64-bit masks to arrays

examples/power: change 64-bit masks to arrays

vm_power_manager currently makes use of uint64_t masks to keep track of
cores in use, limiting use of the app to only being able to manage the
first 64 cores in a multi-core system. Many modern systems have core
counts greater than 64, so this limitation needs to be removed.

This patch converts the relevant 64-bit masks to character arrays.

Signed-off-by: David Hunt <david.hunt@intel.com>
Reviewed-by: Anatoly Burakov <anatoly.burakov@intel.com>