Kernel/Devices: Remove required_mode and device_name methods

These methods are no longer needed because SystemServer is able to
populate the DevFS on its own.

Device absolute_path no longer assume a path to the /dev location,
because it really should not assume any path to a Device node.

Because StorageManagement still needs to know the storage name, we
declare a virtual method only for StorageDevices to override, but this
technique should really be removed later on.

Kernel/Storage/PATADiskDevice.cpp

@@ -41,7 +41,7 @@ void PATADiskDevice::start_request(AsyncBlockDeviceRequest& request)
     m_channel->start_request(request, is_slave(), m_capabilities);
 }
 
-String PATADiskDevice::device_name() const
+String PATADiskDevice::storage_name() const
 {
     return String::formatted("hd{:c}", 'a' + minor());
 }