powerpc/mm: Fix build failures due to arch_reserved_kernel_pages()

With NUMA=n and FA_DUMP=y or PRESERVE_FA_DUMP=y the build fails with:

  arch/powerpc/kernel/fadump.c:1739:22: error: no previous prototype for ‘arch_reserved_kernel_pages’ [-Werror=missing-prototypes]
  1739 | unsigned long __init arch_reserved_kernel_pages(void)
       |                      ^~~~~~~~~~~~~~~~~~~~~~~~~~

The prototype for arch_reserved_kernel_pages() is in include/linux/mm.h,
but it's guarded by __HAVE_ARCH_RESERVED_KERNEL_PAGES. The powerpc
headers define __HAVE_ARCH_RESERVED_KERNEL_PAGES in asm/mmzone.h, which
is not included into the generic headers when NUMA=n.

Move the definition of __HAVE_ARCH_RESERVED_KERNEL_PAGES into asm/mmu.h
which is included regardless of NUMA=n.

Additionally the ifdef around __HAVE_ARCH_RESERVED_KERNEL_PAGES needs to
also check for CONFIG_PRESERVE_FA_DUMP.

Signed-off-by: Michael Ellerman <[email protected]>
Link: https://msgid.link/[email protected]

Author: mpe

arch/powerpc/include/asm/mmu.h

@@ -412,5 +412,9 @@ extern void *abatron_pteptrs[2];
 #include <asm/nohash/mmu.h>
 #endif
 
+#if defined(CONFIG_FA_DUMP) || defined(CONFIG_PRESERVE_FA_DUMP)
+#define __HAVE_ARCH_RESERVED_KERNEL_PAGES
+#endif
+
 #endif /* __KERNEL__ */
 #endif /* _ASM_POWERPC_MMU_H_ */

arch/powerpc/include/asm/mmzone.h

@@ -42,9 +42,6 @@ u64 memory_hotplug_max(void);
 #else
 #define memory_hotplug_max() memblock_end_of_DRAM()
 #endif /* CONFIG_NUMA */
-#ifdef CONFIG_FA_DUMP
-#define __HAVE_ARCH_RESERVED_KERNEL_PAGES
-#endif
 
 #endif /* __KERNEL__ */
 #endif /* _ASM_MMZONE_H_ */