v4l2object: set streamparm for outputs that support it

v4l2object: set streamparm for outputs that support it

Without a specified framerate from the sink, the decoder frame interval
should be set using the framerate of the encoded video stream.
Therefore, the v4l2object should be able to change the framerate on the
output if the V4L2 device accepts it.

This is also necessary for mem2mem encoders so that their bitrate
calculation code may work correctly and they may report the correct
frame duration on the capture queue.

https://bugzilla.gnome.org/show_bug.cgi?id=779466