dm: serial: Replace setparity by setconfig

Replace setparity by more generic setconfig ops
to allow uart parity, bits word length and stop bits
number change.

Adds SERIAL_GET_PARITY/BITS/STOP macros.

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>