powerpc: Fix building of arch/powerpc/mm/mem.o when MEMORY_HOTPLUG=y and SPARSEMEM=n

Currently the kernel fails to build with the above config options with:
  CC      arch/powerpc/mm/mem.o
arch/powerpc/mm/mem.c: In function 'arch_add_memory':
arch/powerpc/mm/mem.c:130: error: implicit declaration of function 'create_section_mapping'

This explicitly includes asm/sparsemem.h in arch/powerpc/mm/mem.c and
moves the guards in include/asm-powerpc/sparsemem.h to protect the
SPARSEMEM specific portions only.
Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/mm/mem.c

@@ -44,6 +44,7 @@
 #include <asm/btext.h>
 #include <asm/tlb.h>
 #include <asm/sections.h>
+#include <asm/sparsemem.h>
 #include <asm/vdso.h>
 #include <asm/fixmap.h>
 

include/asm-powerpc/sparsemem.h

@@ -13,6 +13,8 @@
 #define MAX_PHYSADDR_BITS       44
 #define MAX_PHYSMEM_BITS        44
 
+#endif /* CONFIG_SPARSEMEM */
+
 #ifdef CONFIG_MEMORY_HOTPLUG
 extern void create_section_mapping(unsigned long start, unsigned long end);
 extern int remove_section_mapping(unsigned long start, unsigned long end);
@@ -26,7 +28,5 @@ static inline int hot_add_scn_to_nid(unsigned long scn_addr)
 #endif /* CONFIG_NUMA */
 #endif /* CONFIG_MEMORY_HOTPLUG */
 
-#endif /* CONFIG_SPARSEMEM */
-
 #endif /* __KERNEL__ */
 #endif /* _ASM_POWERPC_SPARSEMEM_H */