libsas-fixes for 3.4-rc4

Regression fixes to stabilize the new workqueue and ata asynchronous
error handling implementation that was merged for v3.4-rc1.

1/ fix regression in sas_drain_work() which was stomping on 'work'
   entries while the workqueue was manipulating them.  User sees
   random crashes when trying to use scsi_transport_sas attributes for
   resets, or during discovery.

2/ (2) longstanding bugs related to the fact that libata (inventor and
   primary host_eh_scheduled user) had built-in assumptions of 1:1
   Scsi_Host-to-ata_port relationship.  The libsas 1:N arrangement
   magnified these problems when it gained async eh and began scheduling
   eh in more scenarios (sas-transports resets) in 3.4-rc1.

3/ lifetime fixes for the rphy since code that has a domain_device
   reference expects to be able to de-reference rphy parameters.

4/ (3) fixes for expander discovery bugs, one a recent regression with
   ata-eh clobbering expander-phy data as it polled leading to system
   crashes, a long standing bug that caused libsas to be
   incompatible with expanders that advertised "PHY_VACANT" in low order
   phy indexes, and a quirk for expanders that sometimes fail to zero
   the sas address when no device is attached.

5/ fix for a long-standing bug whereby hotunplug events during initial
   host scan can cause a system crash

6/ fix for a mvsas regression caused by the new end-device naming in
   libsas making the incorrect assumption that at all phy ids
   exported by an lldd are unique.
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