sched/rt: Add accessors rq_of_rt_se()

Two accessors for RT_GROUP_SCHED and !RT_GROUP_SCHED cases.

Signed-off-by: Kirill Tkhai <tkhai@yandex.ru>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1394835295.18748.32.camel@HP-250-G1-Notebook-PC


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