sched/numa: Allow runtime enabling/disabling of NUMA balance without SCHED_DEBUG

The ability to enable/disable NUMA balancing is not a debugging feature
and should not depend on CONFIG_SCHED_DEBUG.  For example, machines within
a HPC cluster may disable NUMA balancing temporarily for some jobs and
re-enable it for other jobs without needing to reboot.

This patch removes the dependency on CONFIG_SCHED_DEBUG for
kernel.numa_balancing sysctl. The other numa balancing related sysctls
are left as-is because if they need to be tuned then it is more likely
that NUMA balancing needs to be fixed instead.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lkml.kernel.org/r/20210324133916.GQ15768@suse.de