drm/panel: simple: add delays for Innolux AT043TN24

The delays between video data and backlight enable and between backlight
disable and end of video data are given as >= 160 ms in the datasheet.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Tested-by: Marco Franchi <marco.franchi@nxp.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171011125958.23064-3-p.zabel@pengutronix.de