drm/tegra: Implement panel support

Use the DRM panel framework to attach a panel to an output. If the panel
attached to a connector supports supports the backlight brightness
accessors, a property will be available to allow the brightness to be
modified from userspace.

Signed-off-by: Thierry Reding <treding@nvidia.com>
diff --git a/drivers/gpu/drm/tegra/Kconfig b/drivers/gpu/drm/tegra/Kconfig
index 8db9b3b..1b5448c 100644
--- a/drivers/gpu/drm/tegra/Kconfig
+++ b/drivers/gpu/drm/tegra/Kconfig
@@ -6,6 +6,7 @@
 	select TEGRA_HOST1X
 	select DRM_KMS_HELPER
 	select DRM_KMS_FB_HELPER
+	select DRM_PANEL
 	select FB_SYS_FILLRECT
 	select FB_SYS_COPYAREA
 	select FB_SYS_IMAGEBLIT