mm: clean up per architecture MM hook header files

Commit 2ae416b142b6 ("mm: new mm hook framework") introduced an empty
header file (mm-arch-hooks.h) for every architecture, even those which
doesn't need to define mm hooks.

As suggested by Geert Uytterhoeven, this could be cleaned through the use
of a generic header file included via each per architecture
asm/include/Kbuild file.

The PowerPC architecture is not impacted here since this architecture has
to defined the arch_remap MM hook.

Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Suggested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/asm-generic/mm-arch-hooks.h b/include/asm-generic/mm-arch-hooks.h
new file mode 100644
index 0000000..5ff0e51
--- /dev/null
+++ b/include/asm-generic/mm-arch-hooks.h
@@ -0,0 +1,16 @@
+/*
+ * Architecture specific mm hooks
+ */
+
+#ifndef _ASM_GENERIC_MM_ARCH_HOOKS_H
+#define _ASM_GENERIC_MM_ARCH_HOOKS_H
+
+/*
+ * This file should be included through arch/../include/asm/Kbuild for
+ * the architecture which doesn't need specific mm hooks.
+ *
+ * In that case, the generic hooks defined in include/linux/mm-arch-hooks.h
+ * are used.
+ */
+
+#endif /* _ASM_GENERIC_MM_ARCH_HOOKS_H */