add copyright headers

lib/cpu.c

lib/cpu.h

lib/dec/apiwrapper.c

lib/dec/dct.h

lib/dec/decinfo.c

lib/dec/decint.h

lib/dec/decode.c

lib/dec/dequant.c

lib/dec/dequant.h

lib/dec/enquant.h

lib/dec/fragment.c

lib/dec/huffdec.c

lib/dec/huffdec.h

lib/dec/huffman.h

lib/dec/idct.c

lib/dec/idct.h

lib/dec/info.c

lib/dec/internal.c

lib/dec/ocintrin.h

lib/dec/quant.c