drm/exynos/fbdev: do not skip fbdev init if there are no connectors

Since connectors can be created dynamically, fbdev should be initialized
even if there are no connectors at the moment. Otherwise fbdev will
not be created even after connector's appearance.
The patch fixes lack of fbdev on rinato and trats boards.

Fixes: 6afb7721 ("drm/exynos: move connector creation to attach callback")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>