[RegisterConfiguration] Streamline access to arch defaults, simplify Registers.

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 b796a38e54640300bf811529c10ed2ae980e0e73..cc26278c979e8d50d0cf0f5dab71958347ca1b86 100644
--- a/src/arm64/assembler-arm64.h
+++ b/src/arm64/assembler-arm64.h
@@ -154,9 +154,6 @@ struct Register : public CPURegister {
     DCHECK(IsValidOrNone());
   }
 
-  const char* ToString();
-  bool IsAllocatable(RegisterConfiguration::CompilerSelector compiler =
-                         RegisterConfiguration::CRANKSHAFT) const;
   bool IsValid() const {
     DCHECK(IsRegister() || IsNone());
     return IsValidRegister();
@@ -232,9 +229,6 @@ struct FPRegister : public CPURegister {
     DCHECK(IsValidOrNone());
   }
 
-  const char* ToString();
-  bool IsAllocatable(RegisterConfiguration::CompilerSelector compiler =
-                         RegisterConfiguration::CRANKSHAFT) const;
   bool IsValid() const {
     DCHECK(IsFPRegister() || IsNone());
     return IsValidFPRegister();