uboot-phytec

serial: stm32: Add debug uart support

Add support for early debug printf, before the availability of
driver model and device tree support.

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>