mm: export alloc_pages_vma

nouveau is currently using this through an odd hmm wrapper, and I plan
to switch it to the real thing later in this series.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

mm/mempolicy.c

@@ -2098,6 +2098,7 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
 out:
 	return page;
 }
+EXPORT_SYMBOL(alloc_pages_vma);
 
 /**
  * 	alloc_pages_current - Allocate pages.