media: mediatek: vcodec: add decoder command to support stateless decoder

The supported decoder commands are different for stateless and
stateful architectures. Add stateless decoder commands to fix
the v4l2-compliance test error below.

Codec ioctls:
    VIDIOC_ENCODER_CMD returned -1 (Inappropriate ioctl for device)
    VIDIOC_TRY_ENCODER_CMD returned -1 (Inappropriate ioctl for device)
 test VIDIOC_(TRY_)ENCODER_CMD: OK (Not Supported)
    VIDIOC_G_ENC_INDEX returned -1 (Inappropriate ioctl for device)
 test VIDIOC_G_ENC_INDEX: OK (Not Supported)
    VIDIOC_DECODER_CMD returned -1 (Invalid argument)
    VIDIOC_TRY_DECODER_CMD returned -1 (Invalid argument)
    VIDIOC_TRY_DECODER_CMD returned -1 (Invalid argument)
    fail: v4l2-test-codecs.cpp(126): ret
 test VIDIOC_(TRY_)DECODER_CMD: FAIL

Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Sebastian Fricke <sebastian.fricke@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>