IB/ipath: Provide I/O bus speeds for diagnostic purposes

Modern I/O buses like PCIe and HT can be configured for multiple speeds
and widths.  When an ipath HCA seems to have lower than expected
performance, it is very useful to be able to display what the driver
thinks the bus speed is.

Signed-off-by: Dave Olson <dave.olson@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>