serial: stm32: Replace setparity by setconfig

Replace stm32_serial_setparity by stm32_serial_setconfig
which allows to set serial bits number, parity and stop
bits number.
Only parity setting is implemented.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>