Let boards only define the port and pin number of each LEDs. The common
definitions in `stm32_leds.h` will provide `LED<x>_ON`, `LED<x>_OFF`,
`LED<x>_TOGGLE`, `LED<x>_PIN`, `LED<x>_MASK` and `LED<x>_PORT`.
In addition to code de-duplication, this also makes it easier to use
LEDs in GPIO LL, which can be beneficial for super low overhead
debugging output - e.g. when a bug is timing sensitive and `DEBUG()`
would spent to much time for stdio to reproduce a bug.
Peripheral configured:
- 5 UARTs for stdio via STLink, Arduino connector, PMOD connector,
STMOD+ connector and ESP-01 connector
- 1 I2C available on Arduino connector and STMOD+ connector
- 2 SPIs available on Arduino connector and PMOD connector
