Staging: hv: add the Hyper-V virtual bus

This is the virtual bus that all of the Linux Hyper-V drivers use.

Signed-off-by: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>