lavf/mxfdec: support j2k codec with separate/segmented fields layout
lavf/mxfdec: add j2k codec to intra only codecs
lavf/mxfdec: generate ptses for interlaced j2k streams

Packet ptses correspond to field number - 1. This plus dividing by a factor
of 2 the stream time base will output correct ptses for decoded frames
since we need 2 packets for one decoded frame.
lavf/mxfdec: fix codec and stream time base for separate/segmented fields layout

Since two packets are required to decoded a frame, we need to divide by
a factor of 2 the stream time base so output ptses are correct.
lavf/mxfdec: add -field_rate option

Interpret sample rate as field rate for separate/segmented fields layout.