i40evf: add client interface

i40evf: add client interface

In preparation for upcoming RDMA-capable hardware, add a client
interface to the VF driver. This is a slightly-simplified version
of the PF client interface, with the names changed to protect the
innocent.

Due to the nature of the VF<->PF interactions, the client interface
sometimes needs to call back into itself to pass messages. Because
of this, we can't use the coarse-grained locking like the PF's
client interface uses. Instead, we handle all client interactions
in a separate thread so the watchdog can still run and process
virtual channel messages.

Signed-off-by: Mitch Williams <[email protected]>
Signed-off-by: Jesse Brandeburg <[email protected]>
Signed-off-by: Anjali Singhai Jain <[email protected]>
Signed-off-by: Avinash Dayanand <[email protected]>
Tested-by: Andrew Bowers <[email protected]>
Signed-off-by: Jeff Kirsher <[email protected]>