timer MediaTek use upstream compatible

The timers compatible string in upstream is called
mt6577-timer. Add this compatible to the driver.

Signed-off-by: Matthias Brugger <mbrugger@suse.com>
diff --git a/drivers/timer/mtk_timer.c b/drivers/timer/mtk_timer.c
index b5e76bd..e99135e 100644
--- a/drivers/timer/mtk_timer.c
+++ b/drivers/timer/mtk_timer.c
@@ -71,6 +71,7 @@
 
 static const struct udevice_id mtk_timer_ids[] = {
 	{ .compatible = "mediatek,timer" },
+	{ .compatible = "mediatek,mt6577-timer" },
 	{ }
 };