Add support for handling capabilities requests

Change-Id: Id5aa197312c88b0c448dc085d8477ed67da24724
diff --git a/kernel/ethosu_mailbox.h b/kernel/ethosu_mailbox.h
index 0bc5ffb..5cd5e62 100644
--- a/kernel/ethosu_mailbox.h
+++ b/kernel/ethosu_mailbox.h
@@ -114,6 +114,14 @@
 int ethosu_mailbox_version_request(struct ethosu_mailbox *mbox);
 
 /**
+ * ethosu_mailbox_capabilities_request() - Send capabilities request
+ *
+ * Return: 0 on success, else error code.
+ */
+int ethosu_mailbox_capabilities_request(struct ethosu_mailbox *mbox,
+					void *user_arg);
+
+/**
  * ethosu_mailbox_inference() - Send inference
  *
  * Return: 0 on success, else error code.