xfs: cleanup mapping tmpfs folios into the buffer cache

Directly assign b_addr based on the tmpfs folios without a detour
through pages, reuse the folio_put path used for non-tmpfs buffers
and replace all references to pages in comments with folios.

Partially based on a patch from Dave Chinner <dchinner@redhat.com>.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>