mm/gup: Add try_get_folio() and try_grab_folio()

Convert try_get_compound_head() into try_get_folio() and convert
try_grab_compound_head() into try_grab_folio().  Add a temporary
try_grab_compound_head() wrapper around try_grab_folio() to let us
convert callers individually.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>