media: mediatek: vcodec: Skip SOURCE_CHANGE & EOS events for stateless

The stateless decoder API does not specify the usage of SOURCE_CHANGE
and EOF events. These events are used by stateful decoders to signal
changes in the bitstream. They do not make sense for stateless decoders.

Do not handle subscription for these two types of events for stateless
decoder instances. This fixes the last v4l2-compliance error:

Control ioctls:
		fail: v4l2-test-controls.cpp(946): have_source_change || have_eos
	test VIDIOC_(UN)SUBSCRIBE_EVENT/DQEVENT: FAIL

Fixes: 8cdc3794

 ("media: mtk-vcodec: vdec: support stateless API")
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>