Drivers: hv: vmbus: Introduce a function to remove a rescinded offer

In response to a rescind message, we need to remove the channel and the
corresponding device. Cleanup this code path by factoring out the code
to remove a channel.

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

include/linux/hyperv.h

@@ -1226,6 +1226,7 @@ void hv_kvp_onchannelcallback(void *);
 int hv_vss_init(struct hv_util_service *);
 void hv_vss_deinit(void);
 void hv_vss_onchannelcallback(void *);
+void hv_process_channel_removal(struct vmbus_channel *channel, u32 relid);
 
 extern struct resource hyperv_mmio;