[SCSI] libsas: fix wide port hotplug issues

Hotplug of phys which form wide ports simply does not work at the moment.  Fix
this by adding checks at the hotplug points to see if the attached sas address
of the phy already exists (in which case it's part of a wide port) and act
accordingly.

Signed-off-by: Tom Peng <tom_peng@usish.com>
Signed-off-by: Jack Wang <jack_wang@usish.com>
Signed-off-by: Lindar Liu <lindar_liu@usish.com>
Signed-off-by: Kevin Ao <aoqingyun@usish.com>
[jejb: tidied up coding, fixed an error case and made TRUE/FALSE lower
 case to fix a ppc64 compile error in linux-next]
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>