mm: add kernel-doc for folio_mark_accessed()

Convert the existing documentation to kernel-doc and remove references to
pages.

Link: https://lkml.kernel.org/r/20240424191914.361554-7-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>