The optimizations of mipsdsp are not supported by all loongson cpu.
The optimizations of mipsfpu and mipsdspr2 maybe supported by 3A2000/3A3000/3A4000 but not tested yet.
Loongson only support mmi (loongSIMD) optimizations now.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>