Fix google-build-using-namespace warnings in cpu_ref.

* Remove "using namespace ..." statements.
* Replace them with using declarations of the required names.
* Enclose the C++ methods and static and extern "C" functions with
  namespace android and renderscript.
* Keep global C++ functions as-is and add using declarations for them.

Bug: 32670901
Test: build with WITH_TIDY=1
Change-Id: I818de466e8786a6c4f9ce0cd8e0fe027f34d7fad
diff --git a/cpu_ref/rsCpuScriptGroup.cpp b/cpu_ref/rsCpuScriptGroup.cpp
index 9cc9b69..f7a330a 100644
--- a/cpu_ref/rsCpuScriptGroup.cpp
+++ b/cpu_ref/rsCpuScriptGroup.cpp
@@ -19,8 +19,8 @@
 #include "rsScriptGroup.h"
 #include "rsCpuScriptGroup.h"
 
-using namespace android;
-using namespace android::renderscript;
+namespace android {
+namespace renderscript {
 
 CpuScriptGroupImpl::CpuScriptGroupImpl(RsdCpuReferenceImpl *ctx, const ScriptGroupBase *sg) {
     mCtx = ctx;
@@ -294,3 +294,6 @@
         }
     }
 }
+
+} // namespace renderscript
+} // namespace android