[kernel] Add capabilities to handles

This change finally adds capabilities to handles. Included changes:

- j6_handle_t is now again 64 bits, with the highest 8 bits being a type
  code, and the next highest 24 bits being the capability mask, so that
  programs can check type/caps without calling the kernel.
- The definitions grammar now includes a `capabilities [ ]` section on
  objects, to list what capabilities are relevant.
- j6/caps.h is auto-generated from object capability lists
- init_libj6 again sets __handle_self and __handle_sys, this is a bit
  of a hack.
- A new syscall, j6_handle_list, will return the list of existing
  handles owned by the calling process.
- syscall_verify.cpp.cog now actually checks that the needed
  capabilities exist on handles before allowing the call.

scripts/definitions/transformer.py

@@ -1,12 +1,13 @@
 from .parser import Transformer, v_args
 
 def get_opts(args):
-    from .types import CName, Description, Options, Type, UID
+    from .types import Caps, CName, Description, Options, Type, UID
 
     kinds = {
         Description: "desc",
         Options: "opts",
         CName: "cname",
+        Caps: "caps",
         UID: "uid",
         Type: "typename",
     }
@@ -112,6 +113,10 @@ class DefTransformer(Transformer):
         from .types import Options
         return Options([str(s) for s in args])
 
+    def capabilities(self, args):
+        from .types import Caps
+        return Caps([str(s) for s in args])
+
     def description(self, s):
         from .types import Description
         return Description("\n".join(s))
@@ -140,6 +145,9 @@ class DefTransformer(Transformer):
     def COMMENT(self, s):
         return s[2:].strip()
 
+    def OPTION(self, s):
+        return str(s)
+
     def IDENTIFIER(self, s):
         return str(s)