[NDS32] Rewrite cost model.

[NDS32] Rewrite cost model.

gcc/
	* config/nds32/nds32-cost.c (rtx_cost_model_t): New structure.
	(insn_size_16bit, insn_size_32bit): New variables for cost evaluation.
	(nds32_rtx_costs_impl): Simplify.
	(nds32_address_cost_impl): Simplify.
	(nds32_init_rtx_costs): New function.
	(nds32_rtx_costs_speed_prefer): Likewise.
	(nds32_rtx_costs_size_prefer): Likewise.
	(nds32_address_cost_speed_prefer): Likewise.
	(nds32_address_cost_speed_fwprop): Likewise.
	(nds32_address_cost_size_prefer): Likewise.
	* config/nds32/nds32-protos.h (nds32_init_rtx_costs): Declare.
	* config/nds32/nds32.c (nds32_option_override): Use
	nds32_init_rtx_costs function.

Co-Authored-By: Chung-Ju Wu <jasonwucj@gmail.com>
From-SVN: r260411