[kernel] Add handle_clone syscall

Added the handle_clone syscall which allows for cloning a handle with
a subset of the original handle's capabilities.

Related changes:

- srv.init now calls handle_clone on its system handle, and load_program
  was changed to allow this second system handle to be passed to loaded
  programs instead. However, as drv.uart is still a driver AND a log
  reader, this new handle is not actually passed yet.
- The definition parser was using a set for the cap list, which meant
  the order (and thus values) of caps was not static.
- Some code in objects/handle.h was made more explicit about what bits
  meant what.

scripts/definitions/types/object.py

@@ -10,8 +10,7 @@ class Object:
         self.super = typename
         self.methods = children
         self.cname = cname or name
-
-        self.caps = set(caps)
+        self.caps = caps
 
         from . import ObjectRef
         self.__ref = ObjectRef(name)