dev_ns: adopt the backlight lcd subsystem

Adds device namespace awareness to backlight and lcd subsystem - so that
changes to the brightness/power/contrast setttings can only be made from an
active namespace.

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

Change-Id: I5ba918f31d66578a2145200b7f6fdeb842d7ec11
Signed-off-by: Oren Laadan <orenl@cellrox.com>