Support hipHostMallocPortable flag.
Default flags are hipHostMallocPortable | hipHostMallocMapped.
Also:
-refactor tests to move addCount and addCountReverse into HipTest
namespace.
-test multi-GPU host memory.
- Add hierarchy. Tests now live in directories, each with its own
CMakeFiles.txt. Reduces merge conflicts.
- Change make_hip_executable -> build_hip_executable.
- Refresh docs.
- Enable some tests that were previously built but not run.
Change-Id: I8c5de3c954400bf233904282b8b42861a2b7c536