sched: Add sysinterface for GENTLE_FAIR_SLEEPERS

Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
sched: Add controls for sched features

* Currently we provide users attributes to enable/
  disable GENTLE_FAIR_SLEEPERS and ARCH_POWER
* This patch uses already implemented GFS structure
  to add ARCH_POWER attribute.
* Attributes can be found under /sys/kernel/sched/*

Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>