* GPIOF_OPEN_DRAIN - gpio pin is open drain type.
* GPIOF_OPEN_SOURCE - gpio pin is open source type.
+ * GPIOF_EXPORT_DIR_FIXED - export gpio to sysfs, keep direction
+ * GPIOF_EXPORT_DIR_CHANGEABLE - also export, allow changing direction
+
since GPIOF_INIT_* are only valid when configured as output, so group valid
combinations as: