disas/nanomips: Move typedefs etc to nanomips.cpp

disas/nanomips: Move typedefs etc to nanomips.cpp

The following is moved from the nanomips.h to nanomips.cpp file:
- #include line
- typedefs
- enums
- definition of the Pool struct.
Header file nanomips.h will be deleted to be consistent with the rest of
the disas/ code.

Signed-off-by: Milica Lazarevic <milica.lazarevic@syrmia.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220912122635.74032-11-milica.lazarevic@syrmia.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>