Cleanup of affinity hierarchy code.

Some of this is improvement to code suggested by Hal Finkel. Four changes here:
1.Cleanup of hierarchy code to handle all hierarchy cases whether affinity is available or not
2.Separated this and other classes and common functions out to a header file
3.Added a destructor-like fini function for the hierarchy (and call in __kmp_cleanup)
4.Remove some redundant code that is hopefully no longer needed

Differential Revision: http://reviews.llvm.org/D12449