drm/mediatek: dp: Move AUX_P0 setting to mtk_dp_initialize_aux_settings()

Move the register write to MTK_DP_AUX_P0_3690 to set the AUX reply mode
to function mtk_dp_initialize_aux_settings(), as this is effectively
part of the DPTX AUX setup sequence.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20230725073234.55892-6-angelogioacchino.delregno@collabora.com/


Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>