[NDS32] Implement e8 pipeline.

[NDS32] Implement e8 pipeline.

gcc/
	* config.gcc (nds32*-*-*): Check that e8 is valid to --with-cpu.
	* config/nds32/nds32-e8.md: New file.
	* config/nds32/nds32-opts.h (nds32-cpu_type): Add CPU_E8.
	* config/nds32/nds32-pipelines-auxiliary.c: Implementation for e8
	pipeline.
	* config/nds32/nds32-protos.h: More declarations for e8 pipeline.
	* config/nds32/nds32.md (pipeline_model): Add e8.
	* config/nds32/nds32.opt (mcpu): Support e8 pipeline cpus.
	* config/nds32/pipelines.md: Include e8 settings.

Co-Authored-By: Chung-Ju Wu <jasonwucj@gmail.com>
From-SVN: r259220