Loongson 3A4000 and 2k1000 has supported MSA2.0.
This patch optimized SAD_UB2_UH,UNPCK_R_SH_SW,UNPCK_SB_SH and UNPCK_SH_SW with MSA2.0 instruction.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>