Add necessary #include, fixes the warnings:

Add necessary #include, fixes the warnings:
ppc/h264_altivec.c: In function ‘put_h264_qpel16_mc00_altivec’:
ppc/h264_altivec.c:394: warning: implicit declaration of function ‘put_pixels16_altivec’
ppc/h264_altivec.c: In function ‘avg_h264_qpel16_mc00_altivec’:
ppc/h264_altivec.c:395: warning: implicit declaration of function ‘avg_pixels16_altivec’
ppc/h264_altivec.c: In function ‘dsputil_h264_init_ppc’:
ppc/h264_altivec.c:872: warning: implicit declaration of function ‘has_altivec’

Originally committed as revision 11330 to svn://svn.ffmpeg.org/ffmpeg/trunk