sg: add support for VERIFY command using write modes

sg: add support for VERIFY command using write modes

fio does not have an explicit verify data direction and creating a new data
direction just for SCSI VERIFY commands probably is not worthwhile. The format
of SCSI VERIFY commands matches that of write operations since VERIFY commands
can include data transfer to the device. So it seems reasonable to have VERIFY
commands be accounted for as write operations by fio.

Use the sg_write_mode option to support SCSI VERIFY commands with different
BYTCHK values.

BYTCHK	Description
00	No data is transferred to the device; device data is checked
01	Device data is compared with data transferred to device
11	Same as 01 except that only one sector of data is transferred to the
device and each sector specified in the verification extent is compared against
this transferred data.

Also update documentation and add a couple example jobs files.

Signed-off-by: Vincent Fu <vincent.fu@samsung.com>
Link: https://lore.kernel.org/r/20211115200807.117138-2-vincent.fu@samsung.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>