videoctrl: Add pixel_format.

pixel_format is different than pixel_depth.
pixel_format depends on the GPU. A GPU might have multiple formats for the same depth.
We store this in videoctrl so that we can detect changes in pixel_format like we do for pixel_depth and active_width and active_height.

devices/video/videoctrl.h

@@ -82,6 +82,7 @@ protected:
     int         hori_blank = 0;
     int         vert_blank = 0;
     int         pixel_depth;
+    int         pixel_format;
     float       pixel_clock;
     float       refresh_rate;