[RX51] Wire up display blanking + touch screen disable to acpid

There must be some way to turn off power to the display on the RX51. Currently when it is 'off' (when running weston) the backlight is still on. Reducing backlight brightness to 0 doesn't actually turn off the display.

Feel free to assign this one to me (I don't have permission to assign issues), and I plan on tackling this one soon since it obviously impacts battery life.