This fixes a race in `LED<NUM>_TOGGLE`, which is a read-copy-write
operation. Any access to a GPIO pin on the same GPIO port that
happens concurrently could result in data corruption. Using the
GPIO LL API, which is thread-safe, fixes the issue.
Note: The used GPIO LL functions will work even in when the GPIO LL
module is not used.
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.
