ARM: Make use of d16-d31 when available.

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index 06b021669bd1792e150796f844f135935179dbdc..58ad9c980c01358004a7bf55d18fb0bdabc8b160 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -3033,8 +3033,8 @@ void LCodeGen::DoLoadKeyedExternalArray(LLoadKeyed* instr) {
         : Operand(key, LSL, shift_size);
     __ add(scratch0(), external_pointer, operand);
     if (elements_kind == EXTERNAL_FLOAT_ELEMENTS) {
-      __ vldr(result.low(), scratch0(), additional_offset);
-      __ vcvt_f64_f32(result, result.low());
+      __ vldr(kScratchDoubleReg.low(), scratch0(), additional_offset);
+      __ vcvt_f64_f32(result, kScratchDoubleReg.low());
     } else  {  // i.e. elements_kind == EXTERNAL_DOUBLE_ELEMENTS
       __ vldr(result, scratch0(), additional_offset);
     }