media: coda: request to skip kernel mapping for decoded buffers

The kernel driver never touches the decoded buffers with the CPU.
All accesses are either done by hardware DMA masters or userspace
mapping the buffers. This means we don't need a kernel virtual
address mapping for those buffers at all. As those buffers are
usually quite large, we can save a good deal of kernel vmalloc
space by requesting to not have a kernel mapping set up for them.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>