Consolidate file_mips_xxx variables.

gas/
	* config/tc-mips.c (mips_set_options): Rename fp32 field to fp.
	Update fp32 == 0 to fp == 64 and fp32 == 1 to fp != 64 throughout.
	(file_mips_gp32, file_mips_fp32, file_mips_soft_float,
	file_mips_single_float, file_mips_isa, file_mips_arch): Merge into
	one struct...
	(file_mips_opts): Here. New static global. Update throughout.
	(mips_opts): Update defaults for gp32 and fp.