[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.

src/kernel/syscall.h.cog

@@ -13,48 +13,9 @@ ctx = Context(definitions_path)
 ctx.parse("syscalls.def")
 syscalls = ctx.interfaces["syscalls"]
 
+cog.outl(f"constexpr size_t num_syscalls = {len(syscalls.methods)};")
 ]]]*/
 /// [[[end]]]
 
-enum class syscall : uint64_t
-{
-    /*[[[cog code generation
-
-    for id, scope, method in syscalls.methods:
-        if scope:
-            name = f"{scope.name}_{method.name}"
-        else:
-            name = method.name
-        cog.outl(f"{name:20} = {id},")
-
-    ]]]*/
-    //[[[end]]]
-};
-
 void syscall_initialize();
 extern "C" void syscall_enable();
-
-namespace syscalls
-{
-/*[[[cog code generation
-
-for id, scope, method in syscalls.methods:
-    if scope:
-        name = f"{scope.name}_{method.name}"
-    else:
-        name = method.name
-
-    args = []
-    if method.constructor:
-        args.append("j6_handle_t *handle")
-    elif not method.static:
-        args.append("j6_handle_t handle")
-
-    for param in method.params:
-        for type, suffix in param.type.c_names(param.options):
-            args.append(f"{type} {param.name}{suffix}")
-
-    cog.outl(f"""j6_status_t {name} ({", ".join(args)});""")
-]]]*/
-//[[[end]]]
-}