Kernel: Implement basic module unloading :^)

Kernel modules can now be unloaded via a syscall. They get a chance to
run some code of course. Before deallocating them, we call their
"module_fini" symbol.

Userland/modload.cpp

@@ -5,7 +5,7 @@ int main(int argc, char** argv)
 {
     (void)argc;
     (void)argv;
-    const char* path = "/TestModule.o";
+    const char* path = "/mod/TestModule.o";
     int rc = module_load(path, strlen(path));
     if (rc < 0) {
         perror("module_load");