Rework MIPS nop-insertion code, add -mfix-vr4130 [11/11]

[Eric Christopher]

> Tested on mips64{,el}-linux-gnu and mipsisa64{,el}-elf.  OK to install?
> 
> Richard
> 
> 
> 	* config/tc-mips.c (MAX_VR4130_NOPS, MAX_DELAY_NOPS): New macros.
> 	(MAX_NOPS): Bump to 4.
> 	(mips_fix_vr4130): New variable.
> 	(nops_for_vr4130): New function.
> 	(nops_for_insn): Use MAX_DELAY_NOPS rather than MAX_NOPS.  Use
> 	nops_for_vr4130 if working around VR4130 errata.
> 	(OPTION_FIX_VR4130, OPTION_NO_FIX_VR4130): New macros.
> 	(md_longopts): Add -mfix-vr4130 and -mno-fix-vr4130.
> 	(md_parse_option): Handle them.
> 	(md_show_usage): Print them.
> 	* doc/c-mips.texi: Document -mfix-vr4130 and -mno-fix-vr4130.

OK mainline and branch.

-eric