Add av_cold attributes to arch-specific init functions

libavcodec/alpha/dsputil_alpha.c

libavcodec/alpha/mpegvideo_alpha.c

libavcodec/arm/dsputil_init_arm.c

libavcodec/arm/dsputil_init_neon.c

libavcodec/arm/fmtconvert_init_arm.c

libavcodec/arm/h264dsp_init_arm.c

libavcodec/arm/h264pred_init_arm.c

libavcodec/arm/h264qpel_init_arm.c

libavcodec/arm/mpegaudiodsp_init_arm.c

libavcodec/arm/mpegvideo_arm.c

libavcodec/arm/mpegvideo_armv5te.c

libavcodec/arm/rv34dsp_init_arm.c

libavcodec/arm/rv40dsp_init_arm.c

libavcodec/arm/videodsp_init_arm.c

libavcodec/arm/videodsp_init_armv5te.c

libavcodec/arm/vorbisdsp_init_arm.c

libavcodec/arm/vp56dsp_init_arm.c

libavcodec/bfin/dsputil_bfin.c

libavcodec/bfin/mpegvideo_bfin.c

libavcodec/bfin/vp3_bfin.c