media: mediatek: vcodec: Make MM21 the default capture format

Given that only the MM21 capture format is supported by userspace tools
(like gstreamer and libyuv), make it the default capture format.

This allows us to force the MM21 format even when a MM21 and MT21C capable
firmware is available (which is needed while dynamic format switching isn't
implemented in the driver), without causing the following regressions on
v4l2-compliance:

        fail: v4l2-test-formats.cpp(478): pixelformat 3132544d (MT21) for buftype 9 not reported by ENUM_FMT
    test VIDIOC_G_FMT: FAIL
        fail: v4l2-test-formats.cpp(478): pixelformat 3132544d (MT21) for buftype 9 not reported by ENUM_FMT
    test VIDIOC_TRY_FMT: FAIL
        fail: v4l2-test-formats.cpp(478): pixelformat 3132544d (MT21) for buftype 9 not reported by ENUM_FMT
    test VIDIOC_S_FMT: FAIL

Fixes: 7501edef ("media: mediatek: vcodec: Different codec using different capture format")
Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Reviewed-by: Nicolas F. R. A. Prado <nfraprado@collabora.com>
Tested-by: Nicolas F. R. A. Prado <nfraprado@collabora.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>