API: Add binding accessors to generic struct mctp_binding

Rather than have every binding include their own wrappers around
binding<->core functions, introduce an accessor to retrieve the struct
mctp_binding from each.

This means we no longer need the binding-specific registration
callbacks. However, we do now need a ->start callback, to allow bindings
to perform post-registration init.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Change-Id: I6cee9e93f37520f85c155a0ca34017cc0675552c
diff --git a/libmctp-astlpc.h b/libmctp-astlpc.h
index 81f3b1b..92510c6 100644
--- a/libmctp-astlpc.h
+++ b/libmctp-astlpc.h
@@ -29,8 +29,9 @@
 struct mctp_binding_astlpc *mctp_astlpc_init_ops(
 		struct mctp_binding_astlpc_ops *ops,
 		void *ops_data, void *lpc_map);
-void mctp_astlpc_register_bus(struct mctp_binding_astlpc *astlpc,
-		struct mctp *mctp, mctp_eid_t eid);
+
+struct mctp_binding *mctp_binding_astlpc_core(struct mctp_binding_astlpc *b);
+
 int mctp_astlpc_poll(struct mctp_binding_astlpc *astlpc);
 
 /* fileio-based interface */