backlight: Add Samsung LTV350QV LCD driver

This patch adds support for powering on and off the Samsung LTV350QV LCD
panel via SPI.  The driver responds to framebuffer power management, it
powers off the panel on reboot/halt/poweroff.  It can also be controlled
through sysfs.  The panel is powered up when the module is loaded, and off
when the module is unloaded.  Verified on AVR32 STK1000.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Richard Purdie <rpurdie@rpsys.net>