mm/gup: move try_grab_page() to mm/internal.h

This is part of the internal function of gup.c and is only non-static so
that the parts of gup.c in the huge_memory.c and hugetlb.c can call it.

Put it in internal.h beside the similarly purposed try_grab_folio()

Link: https://lkml.kernel.org/r/4-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mm.h

@@ -1268,8 +1268,6 @@ static inline void get_page(struct page *page)
 	folio_get(page_folio(page));
 }
 
-int __must_check try_grab_page(struct page *page, unsigned int flags);
-
 static inline __must_check bool try_get_page(struct page *page)
 {
 	page = compound_head(page);

mm/internal.h

@@ -856,6 +856,7 @@ int migrate_device_coherent_page(struct page *page);
  * mm/gup.c
  */
 struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags);
+int __must_check try_grab_page(struct page *page, unsigned int flags);
 
 extern bool mirrored_kernelcore;