Refactor S390 instruction logging

[matthewhall2]

Z currently uses a big switch-case with typecasting when printing instructions, i.e.

case TR::Instruction::IsRSLb:
            print(log, (TR::S390RSLbInstruction *)instr);
            break;
case TR::Instruction::IsRSY:
            print(log, (TR::S390RSInstruction *)instr);
            break;
case TR::Instruction::IsRX:
            print(log, (TR::S390RXInstruction *)instr);
            break;

which are all defined in omr/compiler/ras/Debug.hpp.

These can all be refactored to TR::Instruction::print overloads.