[libomptarget][nfc] Update remaining uint32 to use lanemask_t

Summary:
[libomptarget][nfc] Update remaining uint32 to use lanemask_t

Update a few functions in the API to use lanemask_t instead of i32. NFC for
nvptx. Also update the ActiveThreads type in DataSharingStateTy.
This removes a lot of #ifdef from the downsteam amdgcn implementation.

Reviewers: ABataev, jdoerfert, grokos, ronlieb, RaviNarayanaswamy

Subscribers: openmp-commits

Tags: #openmp

Differential Revision: https://reviews.llvm.org/D68513

llvm-svn: 373806