Run Zephyr on Micro Bit

Docs: docs.zephyrproject.org/2.7.0/boards/arm/bbc_microbit/doc/index.html

Build worked:but flash failed:Related: mattoppenheim.com/2018/06/24/using-udev-to-remove-the-need-for-sudo-with-the-bbc-microbit

The build also generates a .hex file by default, and we've tried to flash it manually with:but we failed to see it do anything with zephyr/blink_gpio.c, so not sure if the flashing was broken or if the code was broken, or if we didn't find the IO pins correctly.