ieee1394: dump mmapped iso buffers in core files

Currently, core files do not contain the mmapped memory of the video1394
or dv1394 devices, which contain the actual video input, making it
impossible to analyse the cause of abnormal program termination for
image analysis or (de)compression software.  Fix that.

Signed-off-by: Philippe De Muyter <phdm@macqel.be>

Also affects users of the rawiso ioctl API of raw1394.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>