mm/mmzone.h: simplify is_highmem_idx()

There is a lot of historical ifdefery in is_highmem_idx() and its helper
zone_movable_is_highmem() that was required because of two different paths
for nodes and zones initialization that were selected at compile time.

Until commit 3f08a30 ("mm: remove CONFIG_HAVE_MEMBLOCK_NODE_MAP
option") the movable_zone variable was only available for configurations
that had CONFIG_HAVE_MEMBLOCK_NODE_MAP enabled so the test in
zone_movable_is_highmem() used that variable only for such configurations.
For other configurations the test checked if the index of ZONE_MOVABLE
was greater by 1 than the index of ZONE_HIGMEM and then movable zone was
considered a highmem zone.  Needless to say, ZONE_MOVABLE - 1 equals
ZONE_HIGHMEM by definition when CONFIG_HIGHMEM=y.

Commit 3f08a30 ("mm: remove CONFIG_HAVE_MEMBLOCK_NODE_MAP option")
made movable_zone variable always available.  Since this variable is set
to ZONE_HIGHMEM if CONFIG_HIGHMEM is enabled and highmem zone is
populated, it is enough to check whether

	zone_idx == ZONE_MOVABLE && movable_zone == ZONE_HIGMEM

to test if zone index points to a highmem zone.

Remove zone_movable_is_highmem() that is not used anywhere except
is_highmem_idx() and use the test above in is_highmem_idx() instead.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Mike Rapoport <[email protected]>
Reviewed-by: Anshuman Khandual <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/mmzone.h

@@ -982,22 +982,11 @@ static inline void zone_set_nid(struct zone *zone, int nid) {}
 
 extern int movable_zone;
 
-#ifdef CONFIG_HIGHMEM
-static inline int zone_movable_is_highmem(void)
-{
-#ifdef CONFIG_NEED_MULTIPLE_NODES
-	return movable_zone == ZONE_HIGHMEM;
-#else
-	return (ZONE_MOVABLE - 1) == ZONE_HIGHMEM;
-#endif
-}
-#endif
-
 static inline int is_highmem_idx(enum zone_type idx)
 {
 #ifdef CONFIG_HIGHMEM
 	return (idx == ZONE_HIGHMEM ||
-		(idx == ZONE_MOVABLE && zone_movable_is_highmem()));
+		(idx == ZONE_MOVABLE && movable_zone == ZONE_HIGHMEM));
 #else
 	return 0;
 #endif