bus/vmbus: add Hyper-V virtual bus support

bus/vmbus: add Hyper-V virtual bus support

This patch adds support for an additional bus type Virtual Machine BUS
(VMBUS) on Microsoft Hyper-V in Windows 10, Windows Server 2016
and Azure. Most of this code was extracted from FreeBSD and some of
this is from earlier code donated by Brocade.

Only Linux is supported at present, but the code is split
to allow future FreeBSD and Windows support.

The bus support relies on the uio_hv_generic driver from Linux
kernel 4.16. Multiple queue support requires additional sysfs
interfaces which is in kernel 5.0 (a.k.a 4.17).

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>