drm/bridge: it6505: Power on downstream device in .atomic_enable

Send DPCD DP_SET_POWER_D0 command to the monitor in .atomic_enable
callback. Without this command, some monitors won't show up again after
changing the resolution.

Fixes: 46ca7da7 ("drm/bridge: it6505: Send DPCD SET_POWER to downstream")

Signed-off-by: Pin-Yen Lin <treapking@chromium.org>
Reviewed-by: Allen Chen <allen.chen@ite.com.tw>
Fixes: 46ca7da7 ("drm/bridge: it6505: Send DPCD SET_POWER to downstream")
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220714173715.v2.1.I85af54e9ceda74ec69f661852825845f983fc343@changeid