refactor: move firmware workspace under firmware

firmware/libs/kaptan-mavlink/definitions/kaptan.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0"?>
+<mavlink>
+  <!-- The root is the only bindgen input. Feature domains remain independent
+       fragments so their message catalogs can evolve without a monolith. -->
+  <include>kaptan/config.xml</include>
+  <include>kaptan/log.xml</include>
+  <include>kaptan/error.xml</include>
+  <include>kaptan/shutdown.xml</include>
+</mavlink>