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

cpu_ref/rsCpuIntrinsic.cpp

diff --git a/cpu_ref/rsCpuIntrinsic.cpp b/cpu_ref/rsCpuIntrinsic.cpp
index 4cb3f9f..6f642b2 100644
--- a/cpu_ref/rsCpuIntrinsic.cpp
+++ b/cpu_ref/rsCpuIntrinsic.cpp
@@ -17,8 +17,8 @@
 
 #include "rsCpuIntrinsic.h"
 
-using namespace android;
-using namespace android::renderscript;
+namespace android {
+namespace renderscript {
 
 RsdCpuScriptIntrinsic::RsdCpuScriptIntrinsic(RsdCpuReferenceImpl *ctx, const Script *s,
                                              const Element *e, RsScriptIntrinsicID iid)
@@ -119,3 +119,6 @@
     mtls->kernel = mRootPtr;
     mtls->fep.usr = this;
 }
+
+} // namespace renderscript
+} // namespace android