drm/panel: simple: Add display timing support

The simple panel driver's ->get_modes() implementation calculates the
display mode list from the typical timings and the ->get_timings()
implementation returns the timings to the connected encoder for mode
validation and fixup.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
[treding@nvidia.com: select VIDEOMODE_HELPERS]
Signed-off-by: Thierry Reding <treding@nvidia.com>
diff --git a/drivers/gpu/drm/panel/Kconfig b/drivers/gpu/drm/panel/Kconfig
index d845837..6d64c7b 100644
--- a/drivers/gpu/drm/panel/Kconfig
+++ b/drivers/gpu/drm/panel/Kconfig
@@ -11,6 +11,7 @@
 	tristate "support for simple panels"
 	depends on OF
 	depends on BACKLIGHT_CLASS_DEVICE
+	select VIDEOMODE_HELPERS
 	help
 	  DRM panel driver for dumb panels that need at most a regulator and
 	  a GPIO to be powered up. Optionally a backlight can be attached so