lib: Introduce generic list_sort function

There are two copies of list_sort() in the tree already, one in the DRM
code, another in ubifs.  Now XFS needs this as well.  Create a generic
list_sort() function from the ubifs version and convert existing users
to it so we don't end up with yet another copy in the tree.

Signed-off-by: Dave Chinner <david@fromorbit.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Acked-by: Artem Bityutskiy <dedekind@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/lib/Makefile b/lib/Makefile
index 911b25a..3b0b4a6 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -21,7 +21,7 @@
 
 obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
 	 bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \
-	 string_helpers.o gcd.o
+	 string_helpers.o gcd.o list_sort.o
 
 ifeq ($(CONFIG_DEBUG_KOBJECT),y)
 CFLAGS_kobject.o += -DDEBUG