Optimize theora decoding with msa in functions:
1. ff_vp3_idct_add_msa
2. ff_vp3_idct_put_msa
3. ff_vp3_idct_dc_add_msa
4. ff_vp3_v_loop_filter_msa
5. ff_vp3_h_loop_filter_msa
6. ff_put_no_rnd_pixels_l2_msa

Theora decoding speed improved about 36%(from 22fps to 30fps, Tested on loongson 2K1000).
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>