omxbufferpool: make video stride and offset calculation easier
omxbufferpool: make video stride and offset calculation easier

It will be easier to support more color format.

GStreamer/gst-omx,renesas-rcar/gst-omx,freedesktop-unofficial-mirror/gstreamer__gst-omx,leio/gst-omx,CapOM/gst-omx,surround-io/gst-omx,pliu6/gst-omx,GStreamer/gst-omx,GStreamer/gst-omx,renesas-rcar/gst-omx,varunkumara/test-repo,CapOM/gst-omx,CapOM/gst-omx,surround-io/gst-omx,renesas-rcar/gst-omx,freedesktop-unofficial-mirror/gstreamer__gst-omx,pliu6/gst-omx,leio/gst-omx,varunkumara/test-repo,ismelykh/gst-omx-deinterlace,varunkumara/test-repo,ismelykh/gst-omx-deinterlace