drm/tegra: Add support for panel prepare and unprepare routines

Modify tegra output driver to support the new panel calls:
prepare and unprepare.

Signed-off-by: Ajay Kumar <ajaykumar.rs@samsung.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
diff --git a/drivers/gpu/drm/tegra/output.c b/drivers/gpu/drm/tegra/output.c
index a3e4f1e..9609bc3 100644
--- a/drivers/gpu/drm/tegra/output.c
+++ b/drivers/gpu/drm/tegra/output.c
@@ -140,7 +140,9 @@
 	if (mode != DRM_MODE_DPMS_ON) {
 		drm_panel_disable(panel);
 		tegra_output_disable(output);
+		drm_panel_unprepare(panel);
 	} else {
+		drm_panel_prepare(panel);
 		tegra_output_enable(output);
 		drm_panel_enable(panel);
 	}