UBIFS: Implement read-only UBIFS support in U-Boot

The U-Boot UBIFS implementation is largely a direct copy from the current
Linux version (2.6.29-rc6). As already done in the UBI version we have an
"abstraction layer" to redefine or remove some OS calls (e.g. mutex_lock()
...). This makes it possible to use the original Linux code with very
little changes. And by this we can better update to later Linux versions.

I removed some of the Linux features that are not used in the U-Boot
version (e.g. garbage-collection, write support).

Signed-off-by: Stefan Roese <sr@denx.de>
CC: Artem Bityutskiy <dedekind@infradead.org>
CC: Adrian Hunter <ext-Adrian.Hunter@nokia.com>
diff --git a/fs/Makefile b/fs/Makefile
index 8bbd563..22aad12 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -29,6 +29,7 @@
 subdirs-$(CONFIG_CMD_JFFS2) += jffs2
 subdirs-$(CONFIG_CMD_REISER) += reiserfs
 subdirs-$(CONFIG_YAFFS2) += yaffs2
+subdirs-$(CONFIG_CMD_UBIFS) += ubifs
 
 SUBDIRS	:= $(subdirs-y)