omxvideoenc: adjust stride and slice height from input

omxvideoenc: adjust stride and slice height from input

Use the stride and slice height information from the first buffer meta
data to adjust the settings of the input port.
This will ensure that the OMX input buffers match the GStreamer ones
and so will save us from having to copy line-by-line each one.

This is also the first step to allow the OMX encoder to receive dmabuf.

Tested on rpi and zynqultrascaleplus.

https://bugzilla.gnome.org/show_bug.cgi?id=785967