console: Rename libopencm3 console (separate by STM32 family).

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>
console: Reduce warnings.

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>
console: In-memory console.

gdb can be used to read the log buffer and, in principle, could also
inject characters to be consumed by the console (not that I plan ever,
ever to actually do that).

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>