[SCSI] mptfusion: Support SAS2.0 Devices with SAS1.0 Controllers

SAS1.0 Controller was not able to detect SAS2.0 Expanders due to Link
RATE detection was limited to 1.5 Gbps and 3.0 Gbps for SAS1
controllers. Added detection for 6.0 Gbps link.  Now, user can mix-up
6.0 Gpbs links with SAS1.0 controller.

e.g SAS1.0 HBA <----> SAS2.0 Expander <------> SAS2.0 Expander <--------> SAS1.0 Drive.

Signed-off-by: Kashyap Desai <kashyap.desai@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>