powerpc/ptdump: don't entirely rebuild kernel when selecting CONFIG_PPC_DEBUG_WX

Selecting CONFIG_PPC_DEBUG_WX only impacts ptdump and pgtable_32/64
init calls. Declaring related functions in asm/pgtable.h implies
rebuilding almost everything.

Move ptdump_check_wx() declaration in mm/mmu_decl.h
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/bf34fd9dca61eadf9a134a9f89ebbc162cfd5f86.1578986011.git.christophe.leroy@c-s.fr

arch/powerpc/include/asm/pgtable.h

@@ -94,12 +94,6 @@ void mark_initmem_nx(void);
 static inline void mark_initmem_nx(void) { }
 #endif
 
-#ifdef CONFIG_PPC_DEBUG_WX
-void ptdump_check_wx(void);
-#else
-static inline void ptdump_check_wx(void) { }
-#endif
-
 /*
  * When used, PTE_FRAG_NR is defined in subarch pgtable.h
  * so we are sure it is included when arriving here.

arch/powerpc/mm/mmu_decl.h

@@ -181,3 +181,9 @@ void mmu_mark_rodata_ro(void);
 static inline void mmu_mark_initmem_nx(void) { }
 static inline void mmu_mark_rodata_ro(void) { }
 #endif
+
+#ifdef CONFIG_PPC_DEBUG_WX
+void ptdump_check_wx(void);
+#else
+static inline void ptdump_check_wx(void) { }
+#endif

arch/powerpc/mm/ptdump/ptdump.c

@@ -24,6 +24,8 @@
 #include <asm/page.h>
 #include <asm/pgalloc.h>
 
+#include <mm/mmu_decl.h>
+
 #include "ptdump.h"
 
 /*