V4L/DVB (6054): ivtv: specify some stream sizes in kB instead of MB

Some streams (PCM, VBI decoding) do not need that much memory, so specify
the allocated memory in kB instead of MB to limit memory usage. E.g. 1 MB
is overkill for the VBI decoding stream, 64 kB is enough.

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