Expose the gst_video_info_align function that adds padding and does stride
alignment on a GstVideoInfo. Move this previously private function to
video-info.co
Move the definition of the alignment structure to video.h where it can be picked
up by both the bufferpool and the video-info.
We require the videometa activated before we can implement the alignment of
buffers. Users of the bufferpool should do this manually based on the results of
the allocation query.
