staging: bcm2835-codec: switch to multi-planar API

There are two APIs for mem2mem devices, the older single-planar API and
the newer multi-planar one. Without making things overly complex, the
driver can only support one or the other. However the userspace libv4l2
library has a plugin that allows multi-planar API devices to service
single-planar consumers.

Chromium supports the multi-planar API exclusively, though this is
currently limited to ChromiumOS. It would be possible to add support
for generic Linux.

Switching to the multi-planar API would allow usage of both APIs from
userspace.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>