Impact: do not expose a control that has no effect

Fix to prevent sched_mc_power_saving from being exported through sysfs
on single-socket systems. (Say multicore single socket (Laptop))

CPU core map of the boot cpu should be equal to possible number
of cpus for single socket system.

This fix has been developed at FOSS.in kernel workout.
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>