drm/exynos: dsi: Add support for panel prepare and unprepare routines

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

Signed-off-by: Ajay Kumar <[e-mail]>
Acked-by: Inki Dae <[e-mail]>
Signed-off-by: Thierry Reding <[e-mail]>

drivers/gpu/drm/exynos/exynos_drm_dsi.c

···
 	if (ret < 0)
 		return ret;
 
-	ret = drm_panel_enable(dsi->panel);
+	ret = drm_panel_prepare(dsi->panel);
 	if (ret < 0) {
 		exynos_dsi_poweroff(dsi);
 		return ret;
···
 
 	exynos_dsi_set_display_mode(dsi);
 	exynos_dsi_set_display_enable(dsi, true);
+
+	ret = drm_panel_enable(dsi->panel);
+	if (ret < 0) {
+		exynos_dsi_set_display_enable(dsi, false);
+		drm_panel_unprepare(dsi->panel);
+		exynos_dsi_poweroff(dsi);
+		return ret;
+	}
 
 	dsi->state |= DSIM_STATE_ENABLED;
 
···
 	if (!(dsi->state & DSIM_STATE_ENABLED))
 		return;
 
-	exynos_dsi_set_display_enable(dsi, false);
 	drm_panel_disable(dsi->panel);
+	exynos_dsi_set_display_enable(dsi, false);
+	drm_panel_unprepare(dsi->panel);
 	exynos_dsi_poweroff(dsi);
 
 	dsi->state &= ~DSIM_STATE_ENABLED;