drm/exynos: remove drm_dev from struct exynos_drm_manager

manager-drm_dev is only accessed by exynos_drm_crtc_create() so this patch
pass drm_dev as argument on exynos_drm_crtc_create() and remove it from
struct exynos_drm_manager.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Inki Dae <inki.dae@samsung.com>