[Hexagon] Update AnalyzeBranch, etc target hooks

Improved the AnalyzeBranch, InsertBranch, and RemoveBranch
functions in order to handle more of our branch instructions.
This requires changes to analyzeCompare and PredicateInstructions.
Specifically, we've added support for new value compare jumps,
improved handling of endloop, added more compare instructions,
and improved support for predicate instructions.

Differential Revision: http://reviews.llvm.org/D9559

llvm-svn: 236876