Useful support for YUV videos

Creating videos from YUV is much faster, as debayer can be avoided. Unfortunately, our shader code does not work quite well, so I hacked it to do black&white display without artefacts. I'm enabling YUV by changing libmegapixels:

+++ b/config/pine64,pinephone.conf
@@ -28,7 +28,7 @@ Rear: {
             Width: 1280;
             Height: 720;
             Rate: 30;
-            Format: "BGGR8";
+            Format: "YUYV";
             Rotate: 270;
             FocalLength: 3.33;
             FNumber: 3.0;