Separate io_u from ioengine [2/3] - move io_u functions

Separate io_u from ioengine [2/3] - move io_u functions

Move io_u functions from ioengines.c to io_u.c whose prototypes
are now located in io_u.h after the previous commit.

Prior to the previous commit, ioengine.h originally separated io_u
related function prototypes and ioengine related function prototypes
(by comment) based on whether they invoke struct ioengine_ops member
functions or not. Prototypes for these two functions have existed
in io_u side, thus they should be moved to io_u.c respectively.

Signed-off-by: Tomohiro Kusumi <tkusumi@tuxera.com>
Signed-off-by: Jens Axboe <axboe@fb.com>