fs: Add exofs to Kernel build

- Add exofs to fs/Kconfig under "menu 'Miscellaneous filesystems'"
- Add exofs to fs/Makefile

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
diff --git a/fs/Makefile b/fs/Makefile
index 6e82a30..ba77ef2 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -120,3 +120,4 @@
 obj-$(CONFIG_OCFS2_FS)		+= ocfs2/
 obj-$(CONFIG_BTRFS_FS)		+= btrfs/
 obj-$(CONFIG_GFS2_FS)           += gfs2/
+obj-$(CONFIG_EXOFS_FS)          += exofs/