* config/tc-mips.c: Remove all the mips_NNNN variables; just use

* config/tc-mips.c: Remove all the mips_NNNN variables; just use
mips_cpu instead.
(mips_4650, mips_4010, mips_4100): Variables removed.
start-sanitize-vr4xxx
(mips_4121): Variable removed.
end-sanitize-vr4xxx
start-sanitize-vr4320
(mips_4320): Variable removed.
end-sanitize-vr4320
start-sanitize-cygnus
(mips_5400): Variable removed.
end-sanitize-cygnus
start-sanitize-r5900
(mips_5900): Variable removed.
end-sanitize-r5900
start-sanitize-tx49
(mips_4900): Variable removed.
end-sanitize-tx49
(hilo_interlocks, gpr_interlocks, append_insn, macro_build, macro,
macro2, mips16_macro, mips_ip): Test mips_cpu, not the mips_NNNN
variables.
(md_begin): Don't bother initializing the mips_NNNN variables;
mips_cpu is set, and that's good enough now.
(md_parse_option): Have the -mNNNN options set mips_cpu instead of
the mips_NNNN variable.  The -no-mNNNN flags are now no-ops.
(show): New function, to handle wrapping in the CPU lists.
(md_show_usage): Update lists of -mcpu and -mNNNN switches.