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: NArnd Bergmann <arnd@arndb.de>
Acked-by: NJon Hunter <jonathanh@nvidia.com>
Signed-off-by: NThierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/Kconfig

@@ -3,6 +3,7 @@ config DRM_TEGRA
 	depends on ARCH_TEGRA || (ARM && COMPILE_TEST)
 	depends on COMMON_CLK
 	depends on DRM
+	depends on OF
 	select DRM_KMS_HELPER
 	select DRM_MIPI_DSI
 	select DRM_PANEL