[Hexagon] Add intrinsics for data cache operations

This is the clang part, adding support for
  void __builtin_HEXAGON_Y2_dccleana(void*);
  void __builtin_HEXAGON_Y2_dccleaninva(void*);
  void __builtin_HEXAGON_Y2_dcinva(void*);
  void __builtin_HEXAGON_Y2_dczeroa(void*);
  void __builtin_HEXAGON_Y4_l2fetch(void*, unsigned);
  void __builtin_HEXAGON_Y5_l2fetch(void*, unsigned long long);
Requires r308032.

llvm-svn: 308035