a new way of determining reference motion vector
Using surrounding reconstructed pixels from left and above to select best matching mv to use as reference motion vector for mv encoding. Test results: AVGPSNR GLBPSNR VPXSSIM Derf: 1.107% 1.062% 0.992% Std-hd:1.209% 1.176% 1.029% Change-Id: I8f10e09ee6538c05df2fb9f069abcaf1edb3fca6