boards: arm: add support for nucleo-l031k6 board

Support for the NUCLEO-L031K6 development board with STM32L031K6 SoC.

Although the SoC only contains 32k flash and 8K RAM, it has been tested
on a number of samples and has worked as expected.

Signed-off-by: Steven Daglish <s.c.daglish@gmail.com>
9 files changed