Add the ops for GPIO driver get_dir_flags(), allows to get dynamically
the current gpio configuration; it is used by the API function
dm_gpio_get_dir_flags().

When these optional ops are absent, the gpio uclass continues to use
the mandatory ops (direction_output, direction_input, get_value) and
value of desc->flags to manage only the main dir flags:
- GPIOD_IS_IN
- GPIOD_IS_OUT
- GPIOD_IS_OUT_ACTIVE
- GPIOD_ACTIVE_LOW
Signed-off-by: NPatrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>