PPC/s390: Remove CodeAssembler::LookupExternalReference

Port faf64532

Original Commit Message:

    Indirections for external references are now handled completely in
    macro assemblers, which can produce more efficient code.

R=jgruber@chromium.org, joransiu@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: Ic94019affc7418e2d69944f5d8932502f7912684
Reviewed-on: https://chromium-review.googlesource.com/1099421Reviewed-by: Joran Siu <joransiu@ca.ibm.com>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#53714}

src/compiler/ppc/code-generator-ppc.cc

@@ -2471,7 +2471,7 @@ void CodeGenerator::AssembleMove(InstructionOperand* source,
           __ mov(dst, Operand::EmbeddedNumber(src.ToFloat64().value()));
           break;
         case Constant::kExternalReference:
-          __ mov(dst, Operand(src.ToExternalReference()));
+          __ Move(dst, src.ToExternalReference());
           break;
         case Constant::kHeapObject: {
           Handle<HeapObject> src_object = src.ToHeapObject();

src/compiler/s390/code-generator-s390.cc

@@ -3102,7 +3102,7 @@ void CodeGenerator::AssembleMove(InstructionOperand* source,
           __ mov(dst, Operand::EmbeddedNumber(src.ToFloat64().value()));
           break;
         case Constant::kExternalReference:
-          __ mov(dst, Operand(src.ToExternalReference()));
+          __ Move(dst, src.ToExternalReference());
           break;
         case Constant::kHeapObject: {
           Handle<HeapObject> src_object = src.ToHeapObject();