vmbus: use resource for hyperv mmio region

Use a resource for the hyperv mmio region instead of start/size
variables.  Register the region properly so it shows up in
/proc/iomem.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>