OMAP: LCD LS037V7DW01: Add Backlight driver support

Tested on OMAP3EVM for OMAP3530 and AM/DM 3730.

Signed-off-by: Vaibhav Hiremath <hvaibhav@ti.com>
[tomi.valkeinen@nokia.com: added slab.h include]
[tomi.valkeinen@nokia.com: added dependency to BACKLIGHT_CLASS_DEVICE]
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>