ext/ffmpeg/: Add some more width/height/channels/rate limitations to caps to cater for more automagic negotiation.  A...

Original commit message from CVS:
* ext/ffmpeg/gstffmpegcodecmap.c: (gst_ff_vid_caps_new),
(gst_ff_aud_caps_new), (gst_ffmpeg_codecid_to_caps),
(gst_ffmpeg_codectype_to_caps):
* ext/ffmpeg/gstffmpegcodecmap.h:
* ext/ffmpeg/gstffmpegdec.c: (gst_ffmpegdec_negotiate),
(gst_ffmpegdec_register):
* ext/ffmpeg/gstffmpegenc.c: (gst_ffmpegenc_getcaps),
(gst_ffmpegenc_register):
Add some more width/height/channels/rate limitations to caps
to cater for more automagic negotiation.  Addresses #532422.