Kernel: Make device generate their own names

Besides removing the monolithic DevFSDeviceInode::determine_name()
method, being able to determine a device's name inside the /dev
hierarchy outside of DevFS has its uses.

Kernel/TTY/VirtualConsole.h

@@ -69,6 +69,9 @@ private:
     // ^CharacterDevice
     virtual const char* class_name() const override { return "VirtualConsole"; }
 
+    // ^Device
+    virtual String device_name() const override;
+
     void set_active(bool);
 
     void flush_vga_cursor();