- 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
- Boards using stm32f103xx use the same custom config for xtimer
which relies on the same underlying hardware timers that hang
when sleeping for <20us so spin when approaching that limit.