examples/vm_power: show warning when more than 64 cores

examples/vm_power: show warning when more than 64 cores

When using VM power manager app on systems with more than 64 cores,
app could not run even though user does not use cores 64 or higher.
The problem happens only in that case, in which case it will result
in an undefined behaviour.

Thefere, this patch allows the user to run the app on a system with more
than 64 cores, warning the user not to use cores higher than 64 in the VM(s).

Add new known issue where VM power manager app may not work
in a system with more than 64 cores, in release notes.

Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
Tested-by: Marvin Liu <yong.liu@intel.com>
Acked-by: Sergio Gonzalez Monroy <sergio.gonzalez.monroy@intel.com>