fs/squashfs: new filesystem

Add support for SquashFS filesystem. Right now, it does not support
compression but support for zlib will be added in a follow-up commit.

Signed-off-by: Joao Marcos Costa <joaomarcos.costa@bootlin.com>
diff --git a/fs/Kconfig b/fs/Kconfig
index 1cb9831..620af7f 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -22,4 +22,6 @@
 
 source "fs/yaffs2/Kconfig"
 
+source "fs/squashfs/Kconfig"
+
 endmenu