drm/exynos: Remove the exynos_drm_connector shim

This path removes the exynos_drm_connector code since it was just
passing hooks through display_ops. The individual device drivers are now
responsible for implementing drm_connector directly.

Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>