Staging: hv: Cleanup root device handling

Now we can complete the cleanup of the root device
management - use the pci device as the root device for
all Hyper-V devices. As part of this cleanup get rid
of the root device object from vmbus_driver_context.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Mike Sterling <mike.sterling@microsoft.com>
Signed-off-by: Abhishek Kane <v-abkane@microsoft.com>
Signed-off-by: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>