Export the following functions to public:
- ubi_detach(): this is paired with ubi_part(). One may call this function
to completely clean up the ubi subsystem after using ubi_part().
- ubi_{create,find,remove}_vol: this is a set of functions for volume
management.
The original ubi_remove_vol is renamed to __ubi_remove_vol to allow the new
ubi_remove_vol() being used as a wrapper for __ubi_remove_vol() with volume
name.
Also, comments are added for all exported functions.
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>