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);
+}
+
+}

Kernel/Arch/x86/common/QEMUShutdown.h

@@ -0,0 +1,13 @@
+/*
+ * Copyright (c) 2022, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+namespace Kernel {
+
+void qemu_shutdown();
+
+}

Kernel/CMakeLists.txt

@@ -335,6 +335,7 @@ if ("${SERENITY_ARCH}" STREQUAL "i686" OR "${SERENITY_ARCH}" STREQUAL "x86_64")
 
         Arch/x86/common/ScopedCritical.cpp
         Arch/x86/common/SmapDisabler.cpp
+        Arch/x86/common/QEMUShutdown.cpp
     )
 
     set(KERNEL_SOURCES

Kernel/Panic.cpp

@@ -6,7 +6,9 @@
 
 #include <AK/Format.h>
 #include <Kernel/Arch/Processor.h>
-#include <Kernel/Arch/x86/IO.h>
+#if ARCH(I386) || ARCH(X86_64)
+#    include <Kernel/Arch/x86/common/QEMUShutdown.h>
+#endif
 #include <Kernel/CommandLine.h>
 #include <Kernel/KSyms.h>
 #include <Kernel/Panic.h>
@@ -16,11 +18,11 @@ namespace Kernel {
 
 [[noreturn]] static void __shutdown()
 {
-    // Note: This will invoke QEMU Shutdown, but for other platforms (or emulators),
+#if ARCH(I386) || ARCH(X86_64)
-    // this has no effect on the system, so we still need to halt afterwards.
+    qemu_shutdown();
-    // We also try the Bochs/Old QEMU shutdown method, if the first didn't work.
+#endif
-    IO::out16(0x604, 0x2000);
+    // Note: If we failed to invoke platform shutdown, we need to halt afterwards
-    IO::out16(0xb004, 0x2000);
+    // to ensure no further execution on any CPU still happens.
     Processor::halt();
 }