Added Zephyr RTOS support for Olimexino STM32F3

[dayjaby]

Hey all,

I wanted to let you know that I created a PR for support for the (pretty cool) Olimexino STM32F3 board: https://github.com/zephyrproject-rtos/zephyr/pull/48495

Greetings from Germany
David Jablonski