drm/tegra: Convert to using is_hdmi from display info

Prefer the parsed results for is_hdmi in display info over calling
drm_detect_hdmi_monitor().

Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: linux-tegra@vger.kernel.org
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>