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/SATADiskDevice.cpp

@@ -37,7 +37,7 @@ void SATADiskDevice::start_request(AsyncBlockDeviceRequest& request)
     m_port->start_request(request);
 }
 
-String SATADiskDevice::device_name() const
+String SATADiskDevice::storage_name() const
 {
     return String::formatted("hd{:c}", 'a' + minor());
 }