mm: remove ARCH_IMPLEMENTS_FLUSH_DCACHE_FOLIO

Current best practice is to reuse the name of the function as a define to
indicate that the function is implemented by the architecture.

Link: https://lkml.kernel.org/r/20230802151406.3735276-6-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/util.c

@@ -1119,7 +1119,7 @@ void page_offline_end(void)
 }
 EXPORT_SYMBOL(page_offline_end);
 
-#ifndef ARCH_IMPLEMENTS_FLUSH_DCACHE_FOLIO
+#ifndef flush_dcache_folio
 void flush_dcache_folio(struct folio *folio)
 {
 	long i, nr = folio_nr_pages(folio);