kernel: add missing header for libc++

In file included from src/core/hle/kernel/k_light_lock.cpp:4:
In file included from src/./core/hle/kernel/k_light_lock.h:8:
src/./core/hle/kernel/k_scoped_lock.h:25:51: error: no member named 'addressof' in namespace 'std'
    explicit KScopedLock(T& l) : KScopedLock(std::addressof(l)) {}
                                             ~~~~~^