libata: enable SATA disk fua detection on default

Currently, SATA disk fua detection is disabled on default because most of
devices don't support this feature at that time.  With the development of
technology, more and more SATA disks support this feature.  So now we can enable
this detection on default.

Although fua detection is defined as a kernel module parameter, it is too hard
to set its value because it must be loaded and set before system starts up.
That needs to modify initrd file.  So it is inconvenient for administrator who
needs to manage a huge number of servers.

Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>