drm/exynos: disallow fbdev initialization if no device is connected

This patch adds explicit check if there is a connector with
connected status before fbdev initialization. It prevents creation
of default fbdev 1024x768 which is unusable on panels with bigger resolutions.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>