drm/panel: simple: add bus flags for Innolux AT043TN24

For LCD interface controllers that support configuring polarity of
pixel clock and data enable signal, specify bus flags in the panel
descriptor.

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/20171011125958.23064-2-p.zabel@pengutronix.de