Ensure that all arm kernel configs contain ALT_BREAK_TO_DEBUGGER and not
BREAK_TO_DEBUGGER if they have a serial console (most do). A burst of
serial line noise (such as unplugging a usb serial adapter) can look like
a break and drop a working system into the debugger. The alt break sequence
(<CR>~^B) works fine on both serial and non-serial consoles.