policy: Add support for device alert sliders

* Provide support for alert slider hardware.
* Ability to swap order of alert slider within system setting.
* Enable setting config_hasAlertSlider to true and defining
  proc nodes for state path and UEvent match path.

* Contributors:
thecrazyskull
carlosavignano

TODO> SystemUI integration.

Forward ported to Pie by Sirhc95

Change-Id: I46f594923aedf3445ee9cecb16a90c4963f78a89
Signed-off-by: Jackeagle <jackeagle102@gmail.com>
7 files changed