Change "Vpx" to "Avx"

aomdec.c

aomenc.c

aomenc.h

examples/aom_temporal_svc_encoder.c

examples/decode_to_md5.c

examples/decode_with_drops.c

examples/set_maps.c

examples/simple_decoder.c

examples/simple_encoder.c

examples/twopass_encoder.c

ivfdec.c

ivfdec.h

test/encoder_parms_get_to_decoder.cc

test/test_intra_pred_speed.cc

test/variance_test.cc

test/webm_video_source.h

test/y4m_test.cc

tools_common.c

tools_common.h

video_common.h