Hexagon: Honor __builtin_expect by using branch probabilities.

  * lib/Target/Hexagon/HexagonInstrInfo.cpp (GetDotNewPredOp):
  Given a jump opcode return the right pred.new jump opcode with
  a taken vs not-taken hint based on branch probabilities provided
  by the target independent module.
  * lib/Target/Hexagon/HexagonVLIWPacketizer.cpp: Use the above function.
  * lib/Target/Hexagon/HexagonNewValueJump.cpp(getNewvalueJumpOpcode):
  Enhance existing function use branch probabilities like
  HexagonInstrInfo::GetDotNewPredOp but for New Value (GPR) Jumps.