ARM: OMAP: osk+mistral backlight, power, board specific

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: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>