Mistral-specific:

  - Add PWL-driven LCD backlight device

  - Apply power to the board even when the LCD isn't configured; things
    like EEPROM, temperature sensor, and wakeup switch depend on it.
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NTony Lindgren <tony@atomide.com>