sched/numa: Disable sched_numa_balancing on UMA systems

sched/numa: Disable sched_numa_balancing on UMA systems

Commit 2a1ed24 ("sched/numa: Prefer NUMA hotness over cache hotness")
sets sched feature NUMA to true. However this can enable NUMA hinting
faults on a UMA system.

This commit ensures that NUMA hinting faults occur only on a NUMA system
by setting/resetting sched_numa_balancing.

This commit:

  - Makes sched_numa_balancing common to CONFIG_SCHED_DEBUG and
    !CONFIG_SCHED_DEBUG. Earlier it was only in !CONFIG_SCHED_DEBUG.

  - Checks for sched_numa_balancing instead of sched_feat(NUMA).

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1439290813-6683-3-git-send-email-srikar@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>