Implement ATA part of hotplug.  To avoid probing broken devices over
and over again, disabled devices are not automatically detached.  They
are detached only if probing is requested for the device or the
associated port is offline.  Also, to avoid infinite probing loop,
Each device is probed only once per EH run.

As SATA PHY status is fragile, devices are detached only after it has
used up its recovery chances unless explicitly requested by LLDD or
user (LLDD may request direct detach if, for example, it supports cold
presence detection).
Signed-off-by: Tejun Heo <htejun@gmail.com>