Mailbox queue is a type of control queue that's used for communication
between PF and VF. This patch adds code to initialize, configure and
use mailbox queues.

This patch also adds support to detect and parse SR-IOV capabilities
returned by the hardware.
Signed-off-by: NAnirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: NAndrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>