czechlight-cfg-fs: add YANG install script

Let's move cla-sysrepo's install-yang shell script to this package.
Normally, all the packages would have installed these YANGs by
themselves, but because there's no shared state in rootfs, only
in /cfg, so that's where all these modifications belong

Change-Id: Ia5f4ade46098d66a92d940366659e44f9ea74456
diff --git a/package/cla-sysrepo/Config.in b/package/cla-sysrepo/Config.in
index e9804e6..0a40ee3 100644
--- a/package/cla-sysrepo/Config.in
+++ b/package/cla-sysrepo/Config.in
@@ -9,5 +9,6 @@
 	select BR2_PACKAGE_BOOST
 	select BR2_PACKAGE_CPPCODEC
 	select BR2_PACKAGE_LIBEV
+	select BR2_PACKAGE_CZECHLIGHT_CFG_FS
 	help
 	  Control CzechLight devices over YANG with sysrepo