Move check_intra4x4_pred_mode() back from h264.h to h264.c, the function is just

called once per MB in worst case and doesnt seem to benefit from static inline.
Actually the code might be a hair faster now (0.1% according to my benchmark but
this could be random noise)

Originally committed as revision 21173 to svn://svn.ffmpeg.org/ffmpeg/trunk