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/Storage/RamdiskDevice.h

@@ -50,6 +50,7 @@ public:
 
     // ^DiskDevice
     virtual const char* class_name() const override;
+    virtual String device_name() const override;
 
     bool is_slave() const;