Add the concept of FloatRegister for all platforms.

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 3e8be7d75aa156e63ee4ec63a0fd52f29a01841b..42e89bf3097e38a0952781d2fee52d5ddec7d1e3 100644
--- a/src/ppc/assembler-ppc.h
+++ b/src/ppc/assembler-ppc.h
@@ -109,6 +109,8 @@ namespace internal {
   V(d16) V(d17) V(d18) V(d19) V(d20) V(d21) V(d22) V(d23) \
   V(d24) V(d25) V(d26) V(d27) V(d28) V(d29) V(d30) V(d31)
 
+#define FLOAT_REGISTERS DOUBLE_REGISTERS
+
 #define ALLOCATABLE_DOUBLE_REGISTERS(V)                   \
   V(d1)  V(d2)  V(d3)  V(d4)  V(d5)  V(d6)  V(d7)         \
   V(d8)  V(d9)  V(d10) V(d11) V(d12) V(d15)               \
@@ -238,6 +240,11 @@ struct DoubleRegister {
   int reg_code;
 };
 
+typedef DoubleRegister FloatRegister;
+
+// TODO(ppc) Define SIMD registers.
+typedef DoubleRegister Simd128Register;
+
 #define DECLARE_REGISTER(R) \
   const DoubleRegister R = {DoubleRegister::kCode_##R};
 DOUBLE_REGISTERS(DECLARE_REGISTER)
@@ -283,9 +290,6 @@ const CRegister cr5 = {5};
 const CRegister cr6 = {6};
 const CRegister cr7 = {7};
 
-// TODO(ppc) Define SIMD registers.
-typedef DoubleRegister Simd128Register;
-
 // -----------------------------------------------------------------------------
 // Machine instruction Operands