leds: add LM3533 LED driver

Add sub-driver for the LEDs on National Semiconductor / TI LM3533 lighting
power chips.

The chip provides 256 brightness levels, hardware accelerated blinking as
well as ambient-light-sensor and pwm input control.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Rob Landley <rob@landley.net>
Cc: Samuel Ortiz <sameo@linux.intel.com>
Cc: Jonathan Cameron <jic23@cam.ac.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Bryan Wu <bryan.wu@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>