drm/meson/meson_venc: Relax the supported mode checks

Relax a bit the supported modes list by including also 480x1920 and
400x1280. This was actually tested on real hardware and it works
correctly.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230210-relax_dmt_limits-v2-1-318913f08121@baylibre.com