media: mtk-vcodec: support version 2 of decoder firmware ABI

Add support for decoder firmware version 2, which makes the kernel
responsible for managing the VSI context and is used for stateless
codecs.

Signed-off-by: Alexandre Courbot <acourbot@chromium.org>
Signed-off-by: Tzung-Bi Shih <tzungbi@google.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>