mm: Support fadvise without CONFIG_MMU

Commit d3ac21ca ("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: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NJosh Triplett <josh@joshtriplett.org>

mm/Makefile

@@ -28,8 +28,9 @@ else
 	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