Optimize functions with SIMD instruction for loongson mainly combine_disjoint_xxx_u, combine_disjoint_xxx_ca, combine_conjoint_xxx_u,combine_conjoint_xxx_ca

Signed-off-by: CAI Wanwei <caiwanwei@loongson.cn>
MMX: Optimize function combine_multiply_u and combine_multiply_ca with loongson SIMD instruction

Signed-off-by: CAI Wanwei <caiwanwei@loongson.cn>
MMX: Optimize combine functions with Loongson SIMD instruction.

Include:
	mmx_combine_darken_u, mmx_combine_darken_ca
	mmx_combine_lighten_u, mmx_combine_lighten_ca
	mmx_combine_difference_u, mmx_combine_difference_ca

Signed-off-by: CAI Wanwei <caiwanwei@loongson.cn>