Config double register number as 1 for X87 Turbofan.

src/arm64/assembler-arm64.h

Index: src/arm64/assembler-arm64.h
diff --git a/src/arm64/assembler-arm64.h b/src/arm64/assembler-arm64.h
index 7346648a9b02aed4e8150d7359f7c8c5ce898be7..f7de2f8fbcf5d1518e203941f7e8b2f9976a57bb 100644
--- a/src/arm64/assembler-arm64.h
+++ b/src/arm64/assembler-arm64.h
@@ -282,6 +282,14 @@ struct FPRegister : public CPURegister {
     return NumAllocatableRegisters();
   }
 
+  static int NumAllocatableRegistersForTurbo() {
+    return kMaxNumAllocatableRegisters;
+  }
+
+  static int NumAllocatableAliasedRegistersForTurbo() {
+    return NumAllocatableAliasedRegisters();
+  }
+
   // Return true if the register is one that crankshaft can allocate.
   bool IsAllocatable() const {
     return (Bit() & kAllocatableFPRegisters) != 0;