[PGO] Profile runtime name cleanups

Value profile enumerator change to match LLVM code
ProfData new member field name change to match LLVM code
ProfData member type change to match LLVM code
Do not use lower case for types that are internal to implementation (not exposed to APIs)
There is no functional change. This is a preparation patch to enable more code sharing
in follow up patches

Differential Revision: http://reviews.llvm.org/D14841

llvm-svn: 253700