target/mips: convert to TranslatorOps

target/mips: convert to TranslatorOps

Notes:

- DISAS_TOO_MANY replaces the former "break" in the translation loop.
  However, care must be taken not to overwrite a previous condition
  in is_jmp; that's why in translate_insn we first check is_jmp and
  return if it's != DISAS_NEXT.

- Added an assert in translate_insn, before exiting due to an exception,
  to make sure that is_jmp is set to DISAS_NORETURN (the exception
  generation function always sets it.)

- Added an assert for the default case in is_jmp's switch.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Yongbok Kim <yongbok.kim@mips.com>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>