[PATCH] powerpc: fix create_section_mapping compile warning

0day robot reports that a recent rework of how
memory_add_physaddr_to_nid() and phys_to_target_node() are declared
resulted in the following new compilation warning:

arch/powerpc/mm/mem.c:91:12: warning: no previous prototype for 'create_section_mapping' [-Wmissing-prototypes]
   91 | int __weak create_section_mapping(unsigned long start, unsigned long end,
      |            ^~~~~~~~~~~~~~~~~~~~~~

...fix this by moving the declaration of create_section_mapping()
outside of the CONFIG_NEED_MULTIPLE_NODES ifdef guard, and include an
explicit include of asm/mmzone.h in mem.c. An include of linux/mmzone.h
is not sufficient.

Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <redacted>
Cc: Andrew Morton <akpm@linux-foundation.org>
Reported-by: kernel test robot <redacted>
Signed-off-by: Dan Williams <redacted>
---
 arch/powerpc/include/asm/mmzone.h |    7 +++++--
 arch/powerpc/mm/mem.c             |    1 +
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/mmzone.h b/arch/powerpc/include/asm/mmzone.h
index 177fd18caf83..6cda76b57c5d 100644
--- a/arch/powerpc/include/asm/mmzone.h
+++ b/arch/powerpc/include/asm/mmzone.h

@@ -33,8 +33,6 @@ extern struct pglist_data *node_data[];
 extern int numa_cpu_lookup_table[];
 extern cpumask_var_t node_to_cpumask_map[];
 #ifdef CONFIG_MEMORY_HOTPLUG
-extern int create_section_mapping(unsigned long start, unsigned long end,
-				  int nid, pgprot_t prot);
 extern unsigned long max_pfn;
 u64 memory_hotplug_max(void);
 #else

@@ -48,5 +46,10 @@ u64 memory_hotplug_max(void);
 #define __HAVE_ARCH_RESERVED_KERNEL_PAGES
 #endif
 
+#ifdef CONFIG_MEMORY_HOTPLUG
+extern int create_section_mapping(unsigned long start, unsigned long end,
+				  int nid, pgprot_t prot);
+#endif
+
 #endif /* __KERNEL__ */
 #endif /* _ASM_MMZONE_H_ */

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 01ec2a252f09..3fc325bebe4d 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c

@@ -50,6 +50,7 @@
 #include <asm/rtas.h>
 #include <asm/kasan.h>
 #include <asm/svm.h>
+#include <asm/mmzone.h>
 
 #include <mm/mmu_decl.h>