other filters for gpu

We need to add [here](https://github.com/vais-ral/CCPi-astra/blob/master/Wrappers/Python/ccpi/astra/processors/FBP.py#L94)

``` 
if self.filter_type !='ram-lak' and self.device == 'cpu':
                   raise NotImplementedError('Currently in astra, FDK has only ram-lak available')

```