Using `UART_DEV(0)` (UASRT1) for stdio allows to use the same TTL
adapter that is used for programming via `stm32flash` to be used for
serial, without re-wiring after flashing.
- Created new `bluepill-128kib` as 128KiB version of the `bluepill`
- Created new `blackpill-128kib` as 128KiB version of the `blackpill`
- Updated `openocd.cfg` to allow flashing 128KiB of ROM