backlight: spi driver for LMS283GF05 LCD

ADd support for the SPI part of LMS283GF05 LCD.  The LCD uses SPI for
initialization and powerdown sequences.  No further defails are specified
in the datasheet about the initialization/powerdown sequence, just the
magic numbers that have to be sent over SPI bus.  This LCD can be found in
the Aeronix Zipit Z2 handheld.

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>