[turbofan] Make MachineType a pair of enums.

src/compiler/live-range-separator.cc

Index: src/compiler/live-range-separator.cc
diff --git a/src/compiler/live-range-separator.cc b/src/compiler/live-range-separator.cc
index 23331542421845291be88a169238c4c1046d02a0..42407d8aa1459064942f02cec13d24ee2c416601 100644
--- a/src/compiler/live-range-separator.cc
+++ b/src/compiler/live-range-separator.cc
@@ -45,7 +45,8 @@ void CreateSplinter(TopLevelLiveRange *range, RegisterAllocationData *data,
       data->CreateSpillRangeForLiveRange(range);
     }
     if (range->splinter() == nullptr) {
-      TopLevelLiveRange *splinter = data->NextLiveRange(range->machine_type());
+      TopLevelLiveRange *splinter =
+          data->NextLiveRange(range->representation());
       DCHECK_NULL(data->live_ranges()[splinter->vreg()]);
       data->live_ranges()[splinter->vreg()] = splinter;
       range->SetSplinter(splinter);