Currently, we are using method isPredicable to check opcode of machine instr on PowerPC. However, on other platforms, it's adapted to use isPredicable bit in instruction themselves. And by default, TargetInstrInfo::isPredicable(const MachineInstr&) checks the bit in instr.
This patch only affects opcodes mentioned in current PPCInstrInfo::isPredicable, to minimalize changes. We can add it to more opcodes in future patches.