Re-reland: Remove register index/code indirection

src/arm64/assembler-arm64.cc

Index: src/arm64/assembler-arm64.cc
diff --git a/src/arm64/assembler-arm64.cc b/src/arm64/assembler-arm64.cc
index 37a2f5a29d006f1c753b2a0bb07a1183c1276893..0a1ecda9aa9b7c7883ef4eced453dd3035bd18f8 100644
--- a/src/arm64/assembler-arm64.cc
+++ b/src/arm64/assembler-arm64.cc
@@ -35,6 +35,7 @@
 #include "src/arm64/frames-arm64.h"
 #include "src/base/bits.h"
 #include "src/base/cpu.h"
+#include "src/register-configuration.h"
 
 namespace v8 {
 namespace internal {
@@ -192,8 +193,10 @@ bool RelocInfo::IsInConstantPool() {
 Register GetAllocatableRegisterThatIsNotOneOf(Register reg1, Register reg2,
                                               Register reg3, Register reg4) {
   CPURegList regs(reg1, reg2, reg3, reg4);
-  for (int i = 0; i < Register::NumAllocatableRegisters(); i++) {
-    Register candidate = Register::FromAllocationIndex(i);
+  const RegisterConfiguration* config = RegisterConfiguration::ArchDefault();
+  for (int i = 0; i < config->num_allocatable_double_registers(); ++i) {
+    int code = config->GetAllocatableDoubleCode(i);
+    Register candidate = Register::from_code(code);
     if (regs.IncludesAliasOf(candidate)) continue;
     return candidate;
   }