The RSIZ capabilities tag stores the JPEG 2000 profile. In the case of
broadcast profiles, it also stores the broadcast main level, which
specifies the bit rate.
https://bugzilla.gnome.org/show_bug.cgi?id=782337
And always set the sampling field on the src caps, if necessary guessing a
correct value for it from the colorspace field.
Also, did some cleanup: removed sampling enum - redundant.
https://bugzilla.gnome.org/show_bug.cgi?id=766236