drm/panel: simple: Add missing display timing flags for KOE TX26D202VM0BWA

KOE TX26D202VM0BWA panel spec indicates the DE signal is active high in
timing chart, so add DISPLAY_FLAGS_DE_HIGH flag in display timing flags.
This aligns display_timing with panel_desc.

Fixes: 8a070524

 ("drm/panel: simple: Add support for KOE TX26D202VM0BWA panel")
Signed-off-by: Liu Ying <victor.liu@nxp.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20240624015612.341983-1-victor.liu@nxp.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240624015612.341983-1-victor.liu@nxp.com