Fix highmem PPC build failure

Commit f4112de6b679d84bd9b9681c7504be7bdfb7c7d5 ("mm: introduce
debug_kmap_atomic") broke PPC builds with CONFIG_HIGHMEM=y:

   CC      init/main.o
  In file included from include/linux/highmem.h:25,
                   from include/linux/pagemap.h:11,
                   from include/linux/mempolicy.h:63,
                   from init/main.c:53:
  arch/powerpc/include/asm/highmem.h: In function 'kmap_atomic_prot':
  arch/powerpc/include/asm/highmem.h:98: error: implicit declaration of function 'debug_kmap_atomic'
  In file included from include/linux/pagemap.h:11,
                   from include/linux/mempolicy.h:63,
                   from init/main.c:53:
  include/linux/highmem.h: At top level:
  include/linux/highmem.h:196: warning: conflicting types for 'debug_kmap_atomic'
  include/linux/highmem.h:196: error: static declaration of 'debug_kmap_atomic' follows non-static declaration
  include/asm/highmem.h:98: error: previous implicit declaration of 'debug_kmap_atomic' was here
  make[1]: *** [init/main.o] Error 1
  make: *** [init] Error 2

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Acked-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/highmem.h

@@ -19,8 +19,21 @@ static inline void flush_kernel_dcache_page(struct page *page)
 }
 #endif
 
-#ifdef CONFIG_HIGHMEM
+#include <asm/kmap_types.h>
+
+#if defined(CONFIG_DEBUG_HIGHMEM) && defined(CONFIG_TRACE_IRQFLAGS_SUPPORT)
+
+void debug_kmap_atomic(enum km_type type);
+
+#else
 
+static inline void debug_kmap_atomic(enum km_type type)
+{
+}
+
+#endif
+
+#ifdef CONFIG_HIGHMEM
 #include <asm/highmem.h>
 
 /* declarations for linux/mm/highmem.c */
@@ -44,8 +57,6 @@ static inline void *kmap(struct page *page)
 
 #define kunmap(page) do { (void) (page); } while (0)
 
-#include <asm/kmap_types.h>
-
 static inline void *kmap_atomic(struct page *page, enum km_type idx)
 {
 	pagefault_disable();
@@ -187,16 +198,4 @@ static inline void copy_highpage(struct page *to, struct page *from)
 	kunmap_atomic(vto, KM_USER1);
 }
 
-#if defined(CONFIG_DEBUG_HIGHMEM) && defined(CONFIG_TRACE_IRQFLAGS_SUPPORT)
-
-void debug_kmap_atomic(enum km_type type);
-
-#else
-
-static inline void debug_kmap_atomic(enum km_type type)
-{
-}
-
-#endif
-
 #endif /* _LINUX_HIGHMEM_H */