Kernel: Move all code into the Kernel namespace

Kernel/ACPI/DMIDecoder.cpp

@@ -28,6 +28,8 @@
 #include <Kernel/VM/MemoryManager.h>
 #include <LibBareMetal/StdLib.h>
 
+namespace Kernel {
+
 static DMIDecoder* s_dmi_decoder;
 
 //#define SMBIOS_DEBUG
@@ -274,3 +276,5 @@ char* DMIDecoder::get_smbios_string(SMBIOS::TableHeader&, u8)
     ASSERT_NOT_REACHED();
     return nullptr;
 }
+
+}