staging/bcm2835-codec: Add support for decoding interlaced streams

The video decoder can support decoding interlaced streams, so add
the required plumbing to signal this correctly.

The encoder and ISP do NOT support interlaced data, so trying to
configure an interlaced format on those nodes will be rejected.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>