Attempt to not just register but allocate OpenMP pinned memory using a device

Attempt to not just register but allocate OpenMP pinned memory using a device

... instead of 'mmap' plus attempting to register using a device.

Implemented for nvptx offloading via 'cuMemHostAlloc'.

This re-works og12 commit a5a4800e92773da7126c00a9c79b172494d58ab5
"Attempt to register OpenMP pinned memory using a device instead of 'mlock'".

	include/
	* cuda/cuda.h (cuMemHostRegister, cuMemHostUnregister): Remove.
	libgomp/
	* config/linux/allocator.c (linux_memspace_alloc): Add 'init0'
	formal parameter.  Adjust all users.
	(linux_memspace_alloc, linux_memspace_free): Attempt to allocate
	OpenMP pinned memory using a device instead of 'mmap' plus
	attempting to register using a device.
	* libgomp-plugin.h (GOMP_OFFLOAD_register_page_locked)
	(GOMP_OFFLOAD_unregister_page_locked): Remove.
	(GOMP_OFFLOAD_page_locked_host_alloc)
	(GOMP_OFFLOAD_page_locked_host_free): New.
	* libgomp.h (gomp_register_page_locked)
	(gomp_unregister_page_locked): Remove.
	(gomp_page_locked_host_alloc, gomp_page_locked_host_free): New.
	(struct gomp_device_descr): Remove 'register_page_locked_func',
	'unregister_page_locked_func'.  Add 'page_locked_host_alloc_func',
	'page_locked_host_free_func'.
	* plugin/cuda-lib.def (cuMemHostRegister_v2, cuMemHostRegister)
	(cuMemHostUnregister): Remove.
	* plugin/plugin-nvptx.c (GOMP_OFFLOAD_register_page_locked)
	(GOMP_OFFLOAD_unregister_page_locked): Remove.
	(GOMP_OFFLOAD_page_locked_host_alloc)
	(GOMP_OFFLOAD_page_locked_host_free): New.
	* target.c (gomp_register_page_locked)
	(gomp_unregister_page_locked): Remove.
	(gomp_page_locked_host_alloc, gomp_page_locked_host_free): Add.
	(gomp_load_plugin_for_device): Don't handle
	'register_page_locked', 'unregister_page_locked'.  Handle
	'page_locked_host_alloc', 'page_locked_host_free'.

Suggested-by: Andrew Stubbs <ams@codesourcery.com>