Kernel: Move all code into the Kernel namespace

Kernel/FileSystem/TmpFS.cpp

@@ -28,6 +28,8 @@
 #include <Kernel/Process.h>
 #include <Kernel/Thread.h>
 
+namespace Kernel {
+
 NonnullRefPtr<TmpFS> TmpFS::create()
 {
     return adopt(*new TmpFS);
@@ -397,3 +399,5 @@ void TmpFSInode::one_ref_left()
     // Destroy ourselves.
     fs().unregister_inode(identifier());
 }
+
+}