Rewrite YUV processing pipeline.

Use a 4-channel texture instead for packed YUV data so
every pixel in the texture has all the 4:2:2 color data
available.

src/gles2_debayer.h

@@ -8,10 +8,14 @@
 #define SHADER_DEBAYER_PACKED 2
 #define SHADER_YUV 3
 
+#define TEXTURE_BAYER 1
+#define TEXTURE_YUV 2
+
 typedef struct {
         int format;
         int shader;
         float forward_matrix[9];
+        int texture_mode;
 
         GLuint frame_buffer;
         GLuint program;