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

src/mips64/assembler-mips64.h

Index: src/mips64/assembler-mips64.h
diff --git a/src/mips64/assembler-mips64.h b/src/mips64/assembler-mips64.h
index 0b84812395b1fdadaa834e4aee816959aebb8af7..ac0d14fc3131427e39b25a75b04d529b891311a6 100644
--- a/src/mips64/assembler-mips64.h
+++ b/src/mips64/assembler-mips64.h
@@ -125,9 +125,6 @@ struct Register {
     return r;
   }
 
-  const char* ToString();
-  bool IsAllocatable(RegisterConfiguration::CompilerSelector compiler =
-                         RegisterConfiguration::CRANKSHAFT) const;
   bool is_valid() const { return 0 <= reg_code && reg_code < kNumRegisters; }
   bool is(Register reg) const { return reg_code == reg.reg_code; }
   int code() const {
@@ -176,9 +173,6 @@ struct FPURegister {
   // to number of 32-bit FPU regs, but kNumAllocatableRegisters refers to
   // number of Double regs (64-bit regs, or FPU-reg-pairs).
 
-  const char* ToString();
-  bool IsAllocatable(RegisterConfiguration::CompilerSelector compiler =
-                         RegisterConfiguration::CRANKSHAFT) const;
   bool is_valid() const { return 0 <= reg_code && reg_code < kMaxNumRegisters; }
   bool is(FPURegister reg) const { return reg_code == reg.reg_code; }
   FPURegister low() const {