Add support for inference cancellation

Send cancel inference messages to the ethosu subsystem to abort
inference execution there.  Also mark inference as aborted in the
linux driver stack itself, so pending inference messages are not
resent when resetting the firmware.

Change-Id: I244c2b119fd7995d14e3859815abf2a00c7f0583
diff --git a/kernel/ethosu_mailbox.h b/kernel/ethosu_mailbox.h
index 55d4436..7af0c47 100644
--- a/kernel/ethosu_mailbox.h
+++ b/kernel/ethosu_mailbox.h
@@ -203,4 +203,13 @@
 					struct ethosu_buffer *network,
 					uint32_t network_index);
 
+/**
+ * ethosu_mailbox_cancel_inference() - Send inference cancellation
+ *
+ * Return: 0 on success, else error code.
+ */
+int ethosu_mailbox_cancel_inference(struct ethosu_mailbox *mbox,
+				    void *user_arg,
+				    void *inference_handle);
+
 #endif /* ETHOSU_MAILBOX_H */