mm: vmalloc: refactor vm_area_alloc_pages() function

mm: vmalloc: refactor vm_area_alloc_pages() function

The aim is to simplify and making the vm_area_alloc_pages()
function less confusing as it became more clogged nowadays:

- eliminate a "bulk_gfp" variable and do not overwrite a gfp
  flag for bulk allocator;
- drop __GFP_NOFAIL flag for high-order-page requests on upper
  layer. It becomes less spread between levels when it comes to
  __GFP_NOFAIL allocations;
- add a comment about a fallback path if high-order attempt is
  unsuccessful because for such cases __GFP_NOFAIL is dropped;
- fix a typo in a commit message.

Link: https://lkml.kernel.org/r/20240827190916.34242-1-urezki@gmail.com
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>