ARM: tegra: nexus7: Use panel-lvds as the only panel compatible

Depending on a driver probe order, panel-simple driver may probe first,
which results in this error:

  panel-simple display-panel: Reject override mode: panel has a fixed mode

We don't want to use panel-simple anyways because customized timings are
preferred for Nexus 7, hence remove the panel-simple compatibles from the
panel node.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>