[NDS32] Remove some features and options that are not available yet in nds32 port...

[NDS32] Remove some features and options that are not available yet in nds32 port of GNU binutils package.

gcc/
	* config/nds32/nds32.opt (mforce-fp-as-gp): Remove.
	(mforbid-fp-as-gp): Remove.
	(mex9): Remove.
	* config/nds32/nds32-fp-as-gp.c (nds32_have_prologue_p): Remove.
	(nds32_symbol_load_store_p): Remove.
	(nds32_fp_as_gp_check_available): Clean up implementation.
	* config/nds32/nds32.h (LINK_SPEC): Remove -mforce-as-gp and -mex9
	cases.
	* config/nds32/nds32.c (nds32_asm_file_start): No need to consider
	fp-as-gp and ex9 cases.

From-SVN: r219576