lantiq: ltq-vdsl-app: cleanup Makefile

lantiq: ltq-vdsl-app: cleanup Makefile

- CONFIG_IFX_CLI is unused, couldn't find any reference to this config variable
- use disable-feature instead of enable-feature=no
- reorder configure args to have depending args together
- remove configure args which set the default value
- group enable-model and configure args which enable or disable features that
  are covered by the feature set

The config.log contains the same values as before. The vdsl_cpe_control binary
has the same checksum as before.

Signed-off-by: Mathias Kresin <openwrt@kresin.me>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@47888 3c298f89-4303-0410-b956-a3cf2f4a3e73