[media] v4l: add V4L2_PIX_FMT_Y12 format

Y12 is a grey-scale format with a depth of 12 bits per pixel stored in
16-bit words.

Signed-off-by: Michael Jones <michael.jones@matrix-vision.de>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/Documentation/DocBook/v4l/pixfmt.xml b/Documentation/DocBook/v4l/pixfmt.xml
index c6fdcbb..40af4be 100644
--- a/Documentation/DocBook/v4l/pixfmt.xml
+++ b/Documentation/DocBook/v4l/pixfmt.xml
@@ -696,6 +696,7 @@
     &sub-packed-yuv;
     &sub-grey;
     &sub-y10;
+    &sub-y12;
     &sub-y16;
     &sub-yuyv;
     &sub-uyvy;