cpu: send KOBJ_ONLINE event when enabling cpus

In case some sysfs nodes needs to be labeled with a different label than
sysfs then user needs to be notified when a core is brought back online.

Bug: 29359497
Change-Id: I0395c86e01cd49c348fda8f93087d26f88557c91
Signed-off-by: Thierry Strudel <tstrudel@google.com>
Git-commit: fda281a64c7da7b5c634703d22a240a79c337992
Git-repo: https://android.googlesource.com/kernel/common.git


Signed-off-by: Srinivasarao P <spathi@codeaurora.org>