gpio: add ops to set dir flags

gpio: add ops to set dir flags

Add the ops for GPIO driver set_dir_flags() to set the dir flags.
The user can update the direction and configuration
of each GPIO with a only call to dm_gpio_set_dir_flags() or
dm_gpio_set_dir() and respecting the configuration provided by
device tree (saved in desc->flags).

When these optional ops are absent, the gpio uclass use the mandatory
ops (direction_output, direction_input, get_value) and 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: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>