[SCSI] mptsas: use unnumbered port API and remove driver porttracking

This allows us to be rid of the machinery in mptsas for creating and
tracking port numbers.  Since mptsas is merely inventing the numbers,
the SAS transport class may as well do it instead.

Signed-off-by: Eric Moore <Eric.Moore@lsil.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>