[kernel] Add automatic verification to syscalls

Since we have a DSL for specifying syscalls, we can create a verificaton
method for each syscall that can cover most argument (and eventually
capability) verification instead of doing it piecemeal in each syscall
implementation, which can be more error-prone.

Now a new _syscall_verify_* function exists for every syscall, which
calls the real implementation. The syscall table for the syscall handler
now maps to these verify functions.

Other changes:

- Updated the definition grammar to allow options to have a "key:value"
  style, to eventually support capabilities.
- Added an "optional" option for parameters that says a syscall will
  accept a null value.
- Some bonnibel fixes, as definition file changes weren't always
  properly causing updates in the build dep graph.
- The syscall implementation function signatures are no longer exposed
  in syscall.h. Also, the unused syscall enum has been removed.

scripts/definitions/context.py

@@ -34,6 +34,7 @@ class Context:
         pending = set()
         pending.add(filename)
 
+        from .parser import LarkError
         from .parser import Lark_StandAlone as Parser
         from .transformer import DefTransformer
 
@@ -47,7 +48,16 @@ class Context:
             path = self.find(name)
 
             parser = Parser(transformer=DefTransformer(name))
-            imps, objs, ints = parser.parse(open(path, "r").read())
+
+            try:
+                imps, objs, ints = parser.parse(open(path, "r").read())
+            except LarkError as e:
+                import sys
+                import textwrap
+                print(f"\nError parsing {name}:", file=sys.stderr)
+                print(textwrap.indent(str(e), "    "), file=sys.stderr)
+                sys.exit(1)
+
             objects.update(objs)
             interfaces.update(ints)