lavf/mxfdec: support segmented frame layout as separate fields layout

According to S377M, segmented frame layout is identical to separate
field layout except that the two fields are taken from a single scan
of the incoming image, ie: they are coincident in time. Thus the
resulting frame is progressive.
lavf/mxfdec: support j2k codec with interlaced 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 stream time base for j2k codec with interlaced 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
for j2k codec with separate fields and segmented frame layout.

This option is required to obtain a correct frame since S422M specifies
that the track sample rate could either be the frame rate or the field
rate for separate field layout.

For segmented frame layout, the track sample rate is supposed to be the
frame rate however some sample seems to use it as the field rate.