media: mtk-vcodec: venc: support ENUM_FRAMESIZES on OUTPUT formats

v4l2-compliance requires ENUM_FRAMESIZES to support OUTPUT formats.
Reuse mtk_venc_find_format() to make sure both queues are considered
when serving an ENUM_FRAMESIZES.

[hverkuil: fixed some checkpatch alignment warnings]

Signed-off-by: Alexandre Courbot <acourbot@chromium.org>
Acked-by: Tiffany Lin <tiffany.lin@mediatek.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>