Staging: hv: vmbus_drv: Introduce state in struct vmbus_channel to track util services

In preparation for getting rid of util channel synchronization based on
counting util channels, introduce state in  struct vmbus_channel  to
track util services.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@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>