powerpc/mm: change #include "mmu_decl.h" to <mm/mmu_decl.h>

This patch make inclusion of mmu_decl.h independant of the location
of the file including it.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/pgtable_64.c

@@ -52,7 +52,7 @@
 #include <asm/firmware.h>
 #include <asm/dma.h>
 
-#include "mmu_decl.h"
+#include <mm/mmu_decl.h>
 
 
 #ifdef CONFIG_PPC_BOOK3S_64