dev_ns: adopt the led subsystem

Adds device namespace awareness to LED subsystem - so changes to the brightness
setttings can only be made from an active namespace.

Changelog:
[16-Aug-2013] v1 - initial version

Change-Id: I0a0aeb4547062e98e7dfe28935d5428a3d0bbe6e
Signed-off-by: Oren Laadan <orenl@cellrox.com>