net/iavf: stop PCI probe in DCF mode

net/iavf: stop PCI probe in DCF mode

A new DCF PMD will be introduced, which runs on Intel VF hardware, and
it is a pure software design to control the advance functionality (such
as switch, ACL) for rest of the VFs.

So if the DCF (Device Config Function) mode is specified by the devarg
'cap=dcf', then it will stop the PCI probe in the iavf PMD.

Signed-off-by: Haiyue Wang <haiyue.wang@intel.com>
Reviewed-by: Xiaolong Ye <xiaolong.ye@intel.com>
Acked-by: Jingjing Wu <jingjing.wu@intel.com>
Acked-by: Qi Zhang <qi.z.zhang@intel.com>