Kernel: Add Device base class for CharacterDevice.

..to prepare for adding a BlockDevice class.

Kernel/Device.cpp

@@ -0,0 +1,20 @@
+#include "CharacterDevice.h"
+#include <LibC/errno_numbers.h>
+
+Device::~Device()
+{
+}
+
+RetainPtr<FileDescriptor> Device::open(int& error, int options)
+{
+    return VFS::the().open(*this, error, options);
+}
+
+void Device::close()
+{
+}
+
+int Device::ioctl(Process&, unsigned, unsigned)
+{
+    return -ENOTTY;
+}