drm/exynos: remove module of exynos drm subdrv

The exynos drm driver has several subdrv. They each can be module but it
causes unfixed probe order of exynodr drm driver and each subdrv. It
also needs some weird codes such as exynos_drm_fbdev_reinit and
exynos_drm_mode_group_reinit. This patch can remove weird codes and
clear codes through we doesn't modularity each subdrv.

Also this removes unnecessary codes related module.

Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>