samples: led_ws2812: add example for Everlight B1414

This patch adds a devicetree configuration example for the Everlight
B1414 LED controller.

An overlay for the nucleo_f070rb board is provided. It assumes that
a B1414 LED controller is connected to the PA7 pin (SPI 1 MOSI). The
WS2812 SPI driver is used.

Signed-off-by: Simon Guinot <simon.guinot@seagate.com>
4 files changed