x86: mmx2 ---> mmxext in function names

libavcodec/dct-test.c

libavcodec/dsputil.h

libavcodec/x86/cavsdsp.c

libavcodec/x86/dsputil_mmx.c

libavcodec/x86/dsputil_mmx.h

libavcodec/x86/dsputilenc_mmx.c

libavcodec/x86/fdct.c

libavcodec/x86/h264_qpel.c

libavcodec/x86/h264dsp_init.c

libavcodec/x86/idct_mmx_xvid.c

libavcodec/x86/idct_xvid.h

libavcodec/x86/motion_est.c

libavcodec/x86/mpegvideoenc.c

libavcodec/x86/vc1dsp_mmx.c

libavfilter/x86/gradfun.c

libavfilter/x86/yadif.c

libswscale/utils.c

libswscale/x86/rgb2rgb.c

libswscale/x86/swscale.c

libswscale/x86/yuv2rgb.c