examples/vhost: hpa regions for zero copy

check_hpa_regions, fill_hpa_memory_regions and hpa memory region
data structure are added back from old virtio-net.c.

Add hpa (host physical address) region generation/destroy logic.
gpa<->hpa memory translation regions are generated at new_device,
when a virtio device is ready for packet processing.

Signed-off-by: Huawei Xie <huawei.xie@intel.com>
Acked-by: Changchun Ouyang <changchun.ouyang@intel.com>