Reinstate proper FFmpeg license for all files.

doc/print_options.c

libavcodec/aacpsdsp.c

libavcodec/aacpsdsp.h

libavcodec/ac3enc.h

libavcodec/ac3enc_opts_template.c

libavcodec/adx.c

libavcodec/adx_parser.c

libavcodec/arm/aacpsdsp_init_arm.c

libavcodec/arm/aacpsdsp_neon.S

libavcodec/arm/ac3dsp_arm.S

libavcodec/arm/ac3dsp_armv6.S

libavcodec/arm/ac3dsp_neon.S

libavcodec/arm/dca.h

libavcodec/arm/fft_fixed_neon.S

libavcodec/arm/h264cmc_neon.S

libavcodec/arm/mdct_fixed_neon.S

libavcodec/arm/mpegaudiodsp_fixed_armv6.S

libavcodec/arm/mpegaudiodsp_init_arm.c

libavcodec/arm/neon.S

libavcodec/arm/rv34dsp_neon.S