omxh264dec: implement is_format_change
omxh264dec: implement is_format_change

The omxvideodecoder class only checks some of the caps parameters but if
other fields change such as h264 profile and/or level it wouldn't trigger a
reconfiguration.

https://bugzilla.gnome.org/show_bug.cgi?id=752376

CapOM/gst-omx,varunkumara/test-repo,GStreamer/gst-omx,CapOM/gst-omx,CapOM/gst-omx,GStreamer/gst-omx,varunkumara/test-repo,varunkumara/test-repo,GStreamer/gst-omx