Have you done a rebuild of your autoloads?
composer dump-autoload
After that is done, I believe you should be able to just use the classes without use
first.
EDIT: I don't know these packages but I am not sure they include the Facade classes you mention. Facades are very specific to Laravel 4.
I believe if you remove the aliases then this should work OK:
'Fpdf' => 'itbz\fpdf\Facades\Fpdf',
'Fpdi' => 'itbz\fpdi\Facades\Fpdi',
if you want to then use these classes in your app, you would say:
$fpdi = new \fpdi\FPDI();
$fpdf = new \fpdf\FPDF();
or something like that.