i40evf: virtual channel interface

This PCI-E SR-IOV virtual function (VF) driver is dependant upon the
physical function (PF) driver (i40e) for nearly all of its hardware
configuration. Requests from the VF driver are passed to the PF using
the hardware's Admin Queue.

This patch contains the functionality for communicating with the PF
driver. Because of the delay inherent in this communications channel,
most of the replies from the PF driver are handled asynchronously. The
exceptions are the "send API version" and "get VF config" messages,
which busy-wait because they are done so early during init that
interrupts are not yet configured.

Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>