This patch adds support for the mailbox that connects the PF to the Switch
Management entity.  This mailbox will pass TLV formatted messages between
the two entities by using a pair of shared ring buffers.

The primary use of the mailbox is to configure L2 forwarding addresses,
VLANs, and general resource allocation from the switch.
Signed-off-by: NAlexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>