[nvptx] Remove use of CUDA unified memory in libgomp
libgomp/
* plugin/plugin-nvptx.c (struct cuda_map): New.
(struct ptx_stream): Replace d, h, h_begin, h_end, h_next, h_prev,
h_tail with (cuda_map *) map.
(cuda_map_create): New function.
(cuda_map_destroy): New function.
(map_init): Update to use a linked list of cuda_map objects.
(map_fini): Likewise.
(map_pop): Likewise.
(map_push): Likewise. Return CUdeviceptr instead of void.
(init_streams_for_device): Remove stales references to ptx_stream
members.
(select_stream_for_async): Likewise.
(nvptx_exec): Update call to map_init.
From-SVN: r264397
2049befdd0