Kernel: Move QEMU shutdown code to the x86 subdirectory

QEMU VM shutdown code is really x86 specific, so let's ensure we only
use it when compiling a Kernel for x86 machines.

Kernel/Arch/x86/common/QEMUShutdown.cpp

@@ -0,0 +1,21 @@
+/*
+ * Copyright (c) 2022, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Arch/x86/IO.h>
+#include <Kernel/Arch/x86/common/QEMUShutdown.h>
+
+namespace Kernel {
+
+void qemu_shutdown()
+{
+    // Note: This will invoke QEMU Shutdown, but for other platforms (or emulators),
+    // this has no effect on the system.
+    // We also try the Bochs/Old QEMU shutdown method, if the first didn't work.
+    IO::out16(0x604, 0x2000);
+    IO::out16(0xb004, 0x2000);
+}
+
+}