IB/hfi1: Add special setting for low power AOC

Low power QSFP AOC cables require a different SerDes
Tx PLL bandwidth setting than the default.  The
8051 firmware does not know the details, so the driver
needs to tell the firmware through a special setting.

Reviewed-by: Easwar Hariharan <easwar.hariharan@intel.com>
Signed-off-by: Dean Luick <dean.luick@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>