filesetup: add non O_DIRECT direct I/O support for initial layout setup

filesetup: add non O_DIRECT direct I/O support for initial layout setup

8c43ba62('filesetup: align layout buffer') and
6e344dc3('filesetup: keep OS_O_DIRECT flag when pre-allocating file')
only consider OS with open(O_DIRECT).

This commit adds fio_set_directio() since now OS specific direct I/O
initialization is needed by both real ->fd and temporary ->fd while in
extend_file() to equally support the feature.

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