fix[2228133] pixelflinger ignores the "vertical stride" leading to artifacts when playing back video

we lost the concept of vertical stride when moving video playback to EGLImage.
Here we bring it back in a somewhat hacky-way that will work only for the
softgl/mdp backend.
diff --git a/include/private/opengles/gl_context.h b/include/private/opengles/gl_context.h
index 67c2dd8..26cde38 100644
--- a/include/private/opengles/gl_context.h
+++ b/include/private/opengles/gl_context.h
@@ -32,6 +32,8 @@
 #include <GLES/gl.h>
 #include <GLES/glext.h>
 
+struct android_native_buffer_t;
+
 namespace android {
 
 const unsigned int OGLES_NUM_COMPRESSED_TEXTURE_FORMATS = 10;
@@ -602,7 +604,7 @@
     copybit_device_t*       blitEngine;
     int32_t                 minScale;
     int32_t                 maxScale;
-    buffer_handle_t         drawSurfaceBuffer;
+    android_native_buffer_t* drawSurfaceBuffer;
 };
 
 struct ogles_context_t {