Add tests for new API set_dir_flags and set_dir_flags and associated
code in gpio uclass.

Test support for new flags GPIO_OPEN_DRAIN, GPIO_OPEN_SOURCE
GPIO_PULL_UP and GPIO_PULL_DOWN.
Reviewed-by: NSimon Glass <sjg@chromium.org>
Signed-off-by: NPatrick Delaunay <patrick.delaunay@st.com>