drm/bridge: it6505: Fix the order of DP_SET_POWER commands

Send DP_SET_POWER_D3 command to the downstream before stopping DP, so the
suspend process will not be interrupted by the HPD interrupt. Also modify
the order in .atomic_enable callback to make the callbacks symmetric.

Fixes: 46ca7da7 ("drm/bridge: it6505: Send DPCD SET_POWER to downstream")
Signed-off-by: Pin-yen Lin <treapking@chromium.org>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220830045756.1655954-1-treapking@chromium.org