va: filter refactors and vpp small fix

va: filter: refactor convert_surface() to process()                                                                                                                                                            
                                                                                                                                                                                                               
The idea of this change is to add, in the future,                                                                                                                                                              
process_with_generator(), when multiple input surfaces are processed,                                                                                                                                          
for blending.                                                                                                                                                                                                  

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va: filter: Refactor set_formats() to set_video_info().                                                                                                                                                        

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vapostproc: Don't add video alignment option in buffer pool.                                                                                                                                                   
                                                                                                                                                                                                               
vapostproc will not call gst_buffer_pool_config_set_video_alignment(),                                                                                                                                         
thus this option is not required.