HACK: TI: v4l2_codec2: decoder: default to NV12 output

The AM62P gralloc implementation defaults to NV12 when the
YCBCR_420_888 format is requested.
This is a requirement for using libcamera.

Make sure we configure the video decoder to use the
same pixel format.

Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>