vlib: support Hyper-v/Azure VMBus

This patch adds support for VMBus to the VPP infrastructure.
Since the only device that matters is the netvsc Poll Mode Driver
in DPDK, the infrastructure is much simpler than PCI.

Change-Id: Ie96c897ad9c426716c2398e4528688ce2217419b
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>