media: rkvdec: Disable multicore support

media: rkvdec: Disable multicore support

Similarly to what is done in Hantro, avoid exposing equal video codecs to
userspace. Equal video codecs allow scheduling work between the cores.
For that kernel support is required, which does not yet exist.
Until that is implemented, avoid exposing each core separately to
userspace so that multicore can be added in the future without breaking
userspace ABI.

This currently applies only to RK3588 which has 2 equal VDPU381 decoders,
but will be applied for all SoC supported by rkvdec that has multiple DTS
nodes with the same compatible.

Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Detlev Casanova <detlev.casanova@collabora.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>