leds: add arduino,modulino-smartleds

Add an led_strip driver for the modulino smartleds module. This is a
pluggable I2C board with 8 addressable RGB LEDs

The I2C protocol is implemented on an microcontroller on the modulino
board itself, the firmware for that is open source and can be updated
using an Arduino sketch:

Link: https://github.com/arduino/node_modulino_firmware
Link: https://github.com/arduino-libraries/Modulino


Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>