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

src/ppc/assembler-ppc.h

Index: src/ppc/assembler-ppc.h
diff --git a/src/ppc/assembler-ppc.h b/src/ppc/assembler-ppc.h
index 83a073304e3e91c9b1ec990b619add615b782dbb..24166e3c6e989ef6ada53426234f9ba53e7472be 100644
--- a/src/ppc/assembler-ppc.h
+++ b/src/ppc/assembler-ppc.h
@@ -166,9 +166,6 @@ struct Register {
     Register r = {code};
     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 {
@@ -222,9 +219,6 @@ struct DoubleRegister {
   static const int kNumRegisters = Code::kAfterLast;
   static const int kMaxNumRegisters = kNumRegisters;
 
-  const char* ToString();
-  bool IsAllocatable(RegisterConfiguration::CompilerSelector compiler =
-                         RegisterConfiguration::CRANKSHAFT) const;
   bool is_valid() const { return 0 <= reg_code && reg_code < kNumRegisters; }
   bool is(DoubleRegister reg) const { return reg_code == reg.reg_code; }
   int code() const {