ixgbe: add new bus type for intergrated I/O interface (IOSF)

With this patch we add support for a new bus type ixgbe_bus_type_internal.
X550em devices use IOSF and not PCIe bus so this new type is to accommodate
them.

Signed-off-by: Donald C Skidmore <donald.c.skidmore@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>