V4L/DVB (5733): Blackbird should accept only new cx2341x encoding firmwares

Remove temporary support for older 256 kB firmwares.
ivtv, pvrusb2 and blackbird can now all handle the newer larger firmwares,
so support for the older (buggier) firmware can be removed.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>