stm32/uart: Configure pull-up only on RX and CTS, not TX and RTS.
stm32/uart: Configure pull-up only on RX and CTS, not TX and RTS.

RX and CTS are the input pins and pull-ups are enabled so they don't cause
a problem if left unconnected.  But the output pins don't need a pull up
(they were originally all configured with pull up in commit
8f7491a109a555ca897ae49efe98f4cc2b080311).

If needed, the pull-ups can be disabled in Python using machine.Pin after
the UART is constructed.

See issue #4369.

Signed-off-by: Damien George <99e6b749acbfbe2a596df99e91d24d6e1fdbee00@micropython.org>

adafruit/circuitpython,bvernoux/micropython,bvernoux/micropython,adafruit/circuitpython,adafruit/circuitpython,bvernoux/micropython,adafruit/circuitpython,adafruit/circuitpython,henriknelson/micropython,henriknelson/micropython,bvernoux/micropython,adafruit/circuitpython,henriknelson/micropython,henriknelson/micropython,bvernoux/micropython,henriknelson/micropython