ixgbe: Remove unused PCI bus types

The ixgbe never has as very doubtfully ever will support either
PCI or PCI-X devices.  So remove the unused types from the
ixgbe_bus_type.  Thanks to Alex Duyck for suggesting this.

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>