net/cxgbevf: fix inter-VM traffic when physical link down

net/cxgbevf: fix inter-VM traffic when physical link down

Add force_link_up devargs to always force link as up for VFs.
This enables VFs on the same NIC to send traffic to each other
even when physical link is down.

Also add RTE_PMD_REGISTER_PARAM_STRING to export all supported
devargs.

Fixes: 011ebc236ddc ("net/cxgbe: add skeleton VF driver")
Signed-off-by: Shagun Agrawal <shaguna@chelsio.com>
Signed-off-by: Kumar Sanghvi <kumaras@chelsio.com>
Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>