drm/mediatek: dpi: Only enable dpi after the bridge is enabled

Enabling the dpi too early causes glitches on screen.

Move the call to mtk_dpi_enable() at the end of the bridge_enable
callback to ensure everything is setup properly before enabling dpi.

Fixes: 9e629c17 ("drm/mediatek: Add DPI sub driver")
Signed-off-by: Guillaume Ranquet <granquet@baylibre.com>
Signed-off-by: Bo-Chen Chen <rex-bc.chen@mediatek.com>
Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20220701035845.16458-16-rex-bc.chen@mediatek.com/


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