Kernel: Pass a parameter struct to mount()

This was the last remaining syscall that took a null-terminated string
and figured out how long it was by walking it in kernelspace *shudder*.

Kernel/Syscall.h

@@ -355,6 +355,12 @@ struct SC_rename_params {
     StringArgument new_path;
 };
 
+struct SC_mount_params {
+    StringArgument source;
+    StringArgument target;
+    StringArgument fs_type;
+};
+
 void initialize();
 int sync();