common/rc: decouple xfs_io flink check from xfs_io -T check

common/rc: decouple xfs_io flink check from xfs_io -T check

The 3 tests that _require_xfs_io_command "flink", actually require
O_TMPFILE support and flink command, but the former is far unlikely
to be missing. The test btrfs/058 doesn't even use the flink
command.

When running these tests on a filesystem that does not support
O_TMPFILE (e.g. overlayfs) the result is not very infomative:

 generic/004 1s ... [not run] xfs_io flink failed (old kernel/wrong fs?)

Decouple the requirements for "flink" command and "-T" command line
flag and require the former explicitly in tests that use it.

As a result the report is now more informative:

 generic/004 1s ... [not run] O_TMPFILE is not supported

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>