CX2341X port was always set to 'memory', but 'streaming' is also possible

ivtv uses the memory (DMA) interface with the CX2341X, while pvrusb2 and
cx88-blackbird use the streaming interface. This setting is now selectable
by the driver.
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>