drm/tegra: Add CONFIG_OF dependency

drm/tegra: Add CONFIG_OF dependency

Without CONFIG_OF, we can run into a build error:

drivers/gpu/drm/tegra/dpaux.c:378:20: error: 'pinconf_generic_dt_node_to_map_group' undeclared here (not in a function); did you mean 'pinconf_generic_params'?
  .dt_node_to_map = pinconf_generic_dt_node_to_map_group,
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                    pinconf_generic_params
drivers/gpu/drm/tegra/dpaux.c:379:17: error: 'pinconf_generic_dt_free_map' undeclared here (not in a function); did you mean 'pinconf_generic_params'?

This adds an explicit dependency.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>