[ffvpx] Update ffvp9/ffvp8 to 3.4.2-release

Structure of code was slightly modified so that it should be no longer necessary to re-generate the config_*.h files, greatly simplifying the resync process in the future.

media/ffvpx/libavcodec/hpeldsp.h

@@ -76,6 +76,8 @@ typedef struct HpelDSPContext {
      * @param pixels source
      * @param line_size number of bytes in a horizontal line of block
      * @param h height
+     * @note The size is kept at [4][4] to match the above pixel_tabs and avoid
+     *       out of bounds reads in the motion estimation code.
      */
     op_pixels_func put_no_rnd_pixels_tab[4][4];