V4L/DVB (5069): Fix bttv and friends on 64bit machines with lots of memory

We have a DMA32 zone now, lets use it to make sure the card
can reach the memory we have allocated for the video frame
buffers.

Signed-off-by: Gerds Hoffmann <kraxel@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>