[Clang][OpenMP] New clang/libomptarget map interface: new function signatures, libomptarget-side

This is the libomptarget-side patch which changes the __tgt_* API function signatures in preparation for the new map interface.
Changes are: Device IDs 32bits --> 64bits, Flags 32bits --> 64bits

Differential revision: https://reviews.llvm.org/D40313

llvm-svn: 318790