sched: add a new SD SHARE_POWERLINE flag for sched_domain

This new flag SD SHARE_POWERLINE reflects the sharing of the power rail
between the members of a domain. As this is the current assumption of the
scheduler, the flag is added to all sched_domain

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
backported to Tuna Hybrid kernel by faux123
Signed-off-by: Paul Reioux <reioux@gmail.com>