fs: jffs2: Move SYS_JFFS2_SORT_FRAGMENTS to Kconfig

Move the symbol SYS_JFFS2_SORT_FRAGMENTS to Kconfig and use the only
remaining part of doc/README.JFFS2 that is still relevant and useful to
the help for this option.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/fs/jffs2/Kconfig b/fs/jffs2/Kconfig
index 0e79c34..3bf01cd 100644
--- a/fs/jffs2/Kconfig
+++ b/fs/jffs2/Kconfig
@@ -17,3 +17,15 @@
 	depends on FS_JFFS2
 	help
 	  Enable support for NAND flash as the backing store for JFFS2.
+
+config SYS_JFFS2_SORT_FRAGMENTS
+	bool "Enable JFFS2 sorting of filesystem fragments (SLOW!)"
+	depends on FS_JFFS2
+	help
+	  If you boot from a partition which is mounted writable, and you
+	  update your boot environment by replacing single files on that
+	  partition, you should also define CONFIG_SYS_JFFS2_SORT_FRAGMENTS.
+	  Scanning the JFFS2 filesystem takes *much* longer with this feature,
+	  though.  Sorting is done while inserting into the fragment list,
+	  which is more or less a bubble sort. That algorithm is known to be
+	  O(n^2), thus you should really consider if you can avoid it!