gpio: add function _dm_gpio_set_dir_flags

Introduce the function _dm_gpio_set_dir_flags to set dir flags
without check if the GPIO is reserved.

Separate the reserved check for "set_dir" and "set_dir_flags".

This patch is a preliminary step to add new ops.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>