This adds support for hot adding and removing
expanders, and its associated attached devices.
When there is a change in topology,
the fusion firmware sends the
MPI_EVENT_SAS_DISCOVERY event to the driver.
The driver will read firmware config pages
to determine what changes took place, and refresh
drivers view of the world stored in ioc->sas_topology.

Here is the details of the action the driver does:

(1) Expander Added :  The mptsas_discovery_work
workqueue is called.  Config pages read, and
ioc->sas_topology is refreshed.  The sas_phy_add()
is called for each phy of the expander.  The
expanders attached devices are added via
sas_rphy_add().  Added end devices are handled within
the MPT_ADD_DEVICE logic in  mptsas_hotplug_work
workqueue.

(2) Expander Delete : The sas_rphy_delete() will be
called for the top most compenent of the parent that the
expander is attached to.  The sas_rphy_delete call
will delete all the children phys, rphys, and end devices.
This is handled from mptsas_discovery_work workqueue.
Signed-off-by: Eric Moore <Eric.Moore@lsil.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>