[libomptarget][devicertl] Replace lanemask with uint64 at interface

Use uint64_t for lanemask on all GPU architectures at the interface
with clang. Updates tests. The deviceRTL is always linked as IR so the zext
and trunc introduced for wave32 architectures will fold after inlining.

Simplification partly motivated by amdgpu gfx10 which will be wave32 and
is awkward to express in the current arch-dependant typedef interface.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D108317