avcodec: loongson delete invalid simple idct put and add optimization

Change-Id: I23a36c65915f01a1cf20e317c14b8eaaa62958b4
Signed-off-by: ZhouXiaoyong <zhouxiaoyong@loongson.cn>

Fixes Decoding of http://loongnix.org/ftp/multimedia/testing/nanocore_720p_24fps_mpeg4_ac3_short.avi

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
