[media] videodev2.h: add defines for the VBI field start lines

While working with raw and sliced VBI support in several applications
I noticed that you really need to know the start linenumbers for
each video field in order to correctly convert the start line numbers
reported by v4l2_vbi_format to the line numbers used in v4l2_sliced_vbi_format.

This patch adds four defines that specify the start lines for each
field for both 525 and 625 line standards.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

include/uapi/linux/videodev2.h

@@ -1642,6 +1642,12 @@ struct v4l2_vbi_format {
 #define V4L2_VBI_UNSYNC		(1 << 0)
 #define V4L2_VBI_INTERLACED	(1 << 1)
 
+/* ITU-R start lines for each field */
+#define V4L2_VBI_ITU_525_F1_START (1)
+#define V4L2_VBI_ITU_525_F2_START (264)
+#define V4L2_VBI_ITU_625_F1_START (1)
+#define V4L2_VBI_ITU_625_F2_START (314)
+
 /* Sliced VBI
  *
  *    This implements is a proposal V4L2 API to allow SLICED VBI