UPSTREAM: sched: Add SD_PREFER_SIBLING for SMT level

Add the SD_PREFER_SIBLING flag for SMT level in order to ensure that
the scheduler will place at least one task per core.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Preeti U. Murthy <preeti@linux.vnet.ibm.com>
Cc: Morten.Rasmussen@arm.com
Cc: dietmar.eggemann@arm.com
Cc: efault@gmx.de
Cc: kamalesh@linux.vnet.ibm.com
Cc: linaro-kernel@lists.linaro.org
Cc: nicolas.pitre@linaro.org
Cc: riel@redhat.com
Link: http://lkml.kernel.org/r/1425052454-25797-11-git-send-email-vincent.guittot@linaro.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>

(am from https://patchwork.kernel.org/patch/5901561

)
Signed-off-by: Juri Lelli <juri.lelli@arm.com>

BUG=chromium:48849
TEST=build and boot tested

Change-Id: I9f76da5e5bad337794ee8b84ccaa283904a12233
Reviewed-on: https://chromium-review.googlesource.com/271864


Reviewed-by: Ricky Liang <jcliang@chromium.org>
Tested-by: Ricky Liang <jcliang@chromium.org>
Commit-Queue: Ricky Liang <jcliang@chromium.org>
Trybot-Ready: Ricky Liang <jcliang@chromium.org>