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.
This board is sold by several vendors on AliExpress, Amazon and ebay.
It does not have name, but since it comes in the same form-factor and
color as the Bluepill line of boards, I think it makes sense to use that
name.
Flashing is a bit cumbersome as I always had to press the reset button
in time when OpenOCD tries to connect to the CPU.
There is no dedicated reset pin exposed on the board.
