[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/PipelinePrinter.cpp b/llvm/tools/llvm-mca/PipelinePrinter.cpp
index 8b2157a..18ef45f 100644
--- a/llvm/tools/llvm-mca/PipelinePrinter.cpp
+++ b/llvm/tools/llvm-mca/PipelinePrinter.cpp
@@ -15,6 +15,7 @@
 #include "PipelinePrinter.h"
 #include "Views/View.h"
 
+namespace llvm {
 namespace mca {
 
 void PipelinePrinter::printReport(llvm::raw_ostream &OS) const {
@@ -22,3 +23,4 @@
     V->printView(OS);
 }
 } // namespace mca.
+} // namespace llvm