[NFC][PowerPC] Remove the redundant InstAlias for OR instruction

[ZhangKang]

Summary

We have handle the InstAlias for OR instructions, but we handle it agagin in PPCInstPrinter.cpp.
We can add some InstAlias in PPCInstPrinter.cpp when we can't handle it in td files. But it's obvious that we can handle or
in td files and we have done it.

PPCInstr64Bit.td:930:def : InstAlias<"mr $rA, $rB", (OR8 g8rc:$rA, g8rc:$rB, g8rc:$rB)>;
PPCInstr64Bit.td:931:def : InstAlias<"mr. $rA, $rB", (OR8_rec g8rc:$rA, g8rc:$rB, g8rc:$rB)>;
PPCInstrInfo.td:2488:def : InstAlias<"mr $rA, $rB", (OR gprc:$rA, gprc:$rB, gprc:$rB)>;
PPCInstrInfo.td:2489:def : InstAlias<"mr. $rA, $rB", (OR_rec gprc:$rA, gprc:$rB, gprc:$rB)>;

We should remove the redundant for OR in PPCInstPrinter.cpp.

[steven.zhang]

LGTM.

llvm/lib/Target/PowerPC/MCTargetDesc/PPCInstPrinter.cpp

if (useSubstituteMnemonic) {
       printOperand(MI, 1, O);
       O << ", " << (unsigned int)SH;
 
       printAnnotation(O, Annot);
       return;
     }
   }
 
-  if ((MI->getOpcode() == PPC::OR || MI->getOpcode() == PPC::OR8) &&
-      MI->getOperand(1).getReg() == MI->getOperand(2).getReg()) {
-    O << "\tmr ";
-    printOperand(MI, 0, O);
-    O << ", ";
-    printOperand(MI, 1, O);
-    printAnnotation(O, Annot);
-    return;
-  }
-
   if (MI->getOpcode() == PPC::RLDICR ||
       MI->getOpcode() == PPC::RLDICR_32) {
     unsigned char SH = MI->getOperand(2).getImm();
     unsigned char ME = MI->getOperand(3).getImm();
     // rldicr RA, RS, SH, 63-SH == sldi RA, RS, SH
     if (63-SH == ME) {
       O << "\tsldi ";
       printOperand(MI, 0, O);