mlx4_core: Handle multi-physical function devices

MT26468 (PCI ID 0x6764) devices can expose multiple physical
functions.  The current driver only handles the primary physical
function.  For other functions, the QUERY_FW firmware command will
fail with the CMD_STAT_MULTI_FUNC_REQ error code.  Don't try to drive
such devices, but print a message saying the driver is skipping those
devices rather than just "QUERY_FW command failed."

Signed-off-by: Yevgeny Petrilin <yevgenyp@mellanox.co.il>

[ Rather than keeping unsupported devices bound to the driver, simply
  print a more informative error message and exit - Roland ]

Signed-off-by: Roland Dreier <rolandd@cisco.com>