Optimization of AC3 floating point decoder for MIPS

FFT in MIPS implementation is working iteratively instead
 of "recursively" calling functions for smaller FFT sizes.
Some of DSP and format convert utils functions are also optimized.

Signed-off-by: Nedeljko Babic <nbabic@mips.com>
Reviewed-by: Vitor Sessak <vitor1001@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

doc/mips.txt

@@ -59,6 +59,7 @@ Files that have MIPS copyright notice in them:
       dsputil_mips.c
       fft_mips.c
       fft_table.h
+      fft_init_table.c
       fmtconvert_mips.c
       mpegaudiodsp_mips_fixed.c
       mpegaudiodsp_mips_float.c