add a #define to id_regs.py which indicates name of the instruction

add a #define to id_regs.py which indicates name of the instruction

the c preprocessor cannot cope with detecting what the name of the
instruction is (and when it does, if it is "and" that throws a
compile-error), so as a workaround have id_regs.py create a
#define INSN_ADD, #define INSN_ADD_I etc.