drm/exynos/dsi: make te-gpios optional

DSI forwards te-gpios interrupts to display controller, but if display
controller works in HW-TRIGGER mode this interrupt is not necessary.
Making te-gpios property optional allows to avoid generating spare
interrupts.
And also if panel device node of command mode panel device doesn't provide
te-gpios property then the panel driver failed to probe. This was a critial
issue.

With this patch we can not only get rid of 60 interrupt callbacks per second
but also fix the critial issues.
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_dsi.c

@@ -1335,9 +1335,12 @@ static int exynos_dsi_register_te_irq(struct exynos_dsi *dsi)
 	int te_gpio_irq;
 
 	dsi->te_gpio = of_get_named_gpio(dsi->panel_node, "te-gpios", 0);
+	if (dsi->te_gpio == -ENOENT)
+		return 0;
+
 	if (!gpio_is_valid(dsi->te_gpio)) {
-		dev_err(dsi->dev, "no te-gpios specified\n");
 		ret = dsi->te_gpio;
+		dev_err(dsi->dev, "cannot get te-gpios, %d\n", ret);
 		goto out;
 	}