[llvm-mca] Move namespace mca inside llvm::

Summary: This allows to remove `using namespace llvm;` in those *.cpp files

When we want to revisit the decision (everything resides in llvm::mca::*) in the future, we can move things to a nested namespace of llvm::mca::, to conceptually make them separate from the rest of llvm::mca::*

Reviewers: andreadb, mattd

Reviewed By: andreadb

Subscribers: javed.absar, tschuett, gbedwell, llvm-commits

Differential Revision: https://reviews.llvm.org/D53407

llvm-svn: 345612
diff --git a/llvm/tools/llvm-mca/Views/SchedulerStatistics.h b/llvm/tools/llvm-mca/Views/SchedulerStatistics.h
index 3515546..56dd3af 100644
--- a/llvm/tools/llvm-mca/Views/SchedulerStatistics.h
+++ b/llvm/tools/llvm-mca/Views/SchedulerStatistics.h
@@ -42,6 +42,7 @@
 #include "llvm/MC/MCSubtargetInfo.h"
 #include <map>
 
+namespace llvm {
 namespace mca {
 
 class SchedulerStatistics final : public View {
@@ -86,5 +87,6 @@
   void printView(llvm::raw_ostream &OS) const override;
 };
 } // namespace mca
+} // namespace llvm
 
 #endif