Staging: hv: Eliminate device_id from vm_device

Both device abstractions: vm_device and hv_device maintain state
to reperesent the device instance (and they refer to them by different
names - device_id in vm_device and dev_instance in hv_device).
In preparation for consolidating all device state in
struct hv_device; eliminate device_id from struct vm_device.

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