ceph: Convert writepage_nounlock() to write_folio_nounlock()

ceph: Convert writepage_nounlock() to write_folio_nounlock()

Remove references to page->index, page->mapping, thp_size(),
page_offset() and other page APIs in favour of their more efficient
folio replacements.

Signed-off-by: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Link: https://lore.kernel.org/r/20250217185119.430193-6-willy@infradead.org
Tested-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>