mm: Support fadvise without CONFIG_MMU

Commit d3ac21cacc24790eb45d735769f35753f5b56ceb ("mm: Support compiling
out madvise and fadvise") incorrectly made fadvise conditional on
CONFIG_MMU.  (The merged branch unintentionally incorporated v1 of the
patch rather than the fixed v2.)  Apply the delta from v1 to v2, to
allow fadvise without CONFIG_MMU.

Reported-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Josh Triplett <josh@joshtriplett.org>
diff --git a/mm/Makefile b/mm/Makefile
index fe7a053..2ad574d 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -28,8 +28,9 @@
 	obj-y		+= bootmem.o
 endif
 
+obj-$(CONFIG_ADVISE_SYSCALLS)	+= fadvise.o
 ifdef CONFIG_MMU
-	obj-$(CONFIG_ADVISE_SYSCALLS)	+= fadvise.o madvise.o
+	obj-$(CONFIG_ADVISE_SYSCALLS)	+= madvise.o
 endif
 obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.o