drm/exynos: delay fbdev initialization until an output is connected

In case fbdev is initialized before any output is connected,
fb resolution defaults to 1024x768. After that any output with
bigger resolution is ignored and fbdev is not displayed.
The patch postpones fbdev initialization to avoid such situation.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>