All the existing `machine.UART` tests in extmod and extmod_hardware are
converted to use the new `target_wiring` scheme, which removes a lot of
duplicated board-specific settings.
All the existing boards that were supported by these UART tests now have
their own `target_wiring` file. Some configurations are board specific (eg
NUCLEO_WB55) and others are port specific.
Signed-off-by: Damien George <damien@micropython.org>
