MIPS lacks CS_OPT_SYNTAX_NOREGNAME support

[neuschaefer]

On MIPS, it's somewhat common to have unnamed registers ($0 to $31), but Capstone doesn't currently support unnamed registers on MIPS, even though the general mechanism exists in capstone (CS_OPT_SYNTAX_NOREGNAME).

MipsInstPrinter.c would need to handle CS_OPT_SYNTAX_NOREGNAME, somewhat similar to ARMInstPrinter.c:

// arch/ARM/ARMInstPrinter.c
void ARM_getRegName(cs_struct *handle, int value)
{
        if (value == CS_OPT_SYNTAX_NOREGNAME) {
                handle->get_regname = getRegisterName2;
                handle->reg_name = ARM_reg_name2;;
        } else {
                handle->get_regname = getRegisterName;
                handle->reg_name = ARM_reg_name;;
        }
}

// arch/Mips/MipsInstPrinter.c
static void printRegName(SStream *OS, unsigned RegNo)
{
        SStream_concat(OS, "$%s", getRegisterName(RegNo));
}

What I've seen when dealing with binutils are:

• unnamed registers $0 - $31
• named registers t1, sp, etc.