drm/exynos: enable dvi mode for dvi monitor

Hdmi monitor and dvi monitor can be distinguished with edid.
This patch enables dvi mode if dvi monitor is connected and does
not enable audio feature for dvi mode because dvi has no audio
feature.

Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>