New code for 6.3:

 - Change when the iomap page_done function is called so that we still
   have a locked folio in the success case.  This fixes a writeback race
   in gfs2.
 - Change when the iomap page_prepare function is called so that gfs2
   can recover from OOM scenarios more gracefully.
 - Rename the iomap page_ops to folio_ops, since they operate on folios
   now.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>