mm: replace PAGE_MIGRATION with IS_ENABLED(CONFIG_MIGRATION)

Since commit 2a11c8ea20bf ("kconfig: Introduce IS_ENABLED(),
IS_BUILTIN() and IS_MODULE()") there is a generic grep-friendly method
for checking config options in C expressions.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/rmap.c b/mm/rmap.c
index c8454e0..78cc46b 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1282,7 +1282,7 @@
 			}
 			dec_mm_counter(mm, MM_ANONPAGES);
 			inc_mm_counter(mm, MM_SWAPENTS);
-		} else if (PAGE_MIGRATION) {
+		} else if (IS_ENABLED(CONFIG_MIGRATION)) {
 			/*
 			 * Store the pfn of the page in a special migration
 			 * pte. do_swap_page() will wait until the migration
@@ -1293,7 +1293,8 @@
 		}
 		set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
 		BUG_ON(pte_file(*pte));
-	} else if (PAGE_MIGRATION && (TTU_ACTION(flags) == TTU_MIGRATION)) {
+	} else if (IS_ENABLED(CONFIG_MIGRATION) &&
+		   (TTU_ACTION(flags) == TTU_MIGRATION)) {
 		/* Establish migration entry for a file page */
 		swp_entry_t entry;
 		entry = make_migration_entry(page, pte_write(pteval));
@@ -1499,7 +1500,7 @@
 		 * locking requirements of exec(), migration skips
 		 * temporary VMAs until after exec() completes.
 		 */
-		if (PAGE_MIGRATION && (flags & TTU_MIGRATION) &&
+		if (IS_ENABLED(CONFIG_MIGRATION) && (flags & TTU_MIGRATION) &&
 				is_vma_temporary_stack(vma))
 			continue;