dm: video: Add a operation to display uclass

The current display class only allow to get timing from edid.
So add a operation to get timing directly from driver.
In driver, I will use fdtdec_decode_display_timing to get timing.

Signed-off-by: Jacob Chen <jacob-chen@iotwrt.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/video/display-uclass.c b/drivers/video/display-uclass.c
index 31522ea..e4763de 100644
--- a/drivers/video/display-uclass.c
+++ b/drivers/video/display-uclass.c
@@ -36,6 +36,9 @@
 	u8 buf[EDID_EXT_SIZE];
 	int ret;
 
+	if (ops && ops->read_timing)
+		return ops->read_timing(dev, timing);
+
 	if (!ops || !ops->read_edid)
 		return -ENOSYS;
 	ret = ops->read_edid(dev, buf, sizeof(buf));