drm: add register and unregister functions for connectors

drm: add register and unregister functions for connectors

Introduce generic functions to register and unregister connectors. This
provides a common place to add and remove associated user space
interfaces.

Signed-off-by: Thomas Wood <thomas.wood@intel.com>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
(cherry picked from commit 34ea3d386347cd6de4c2fa2491dd85c9e753e7e4)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Conflicts:
	drivers/gpu/drm/bridge/ptn3460.c
	drivers/gpu/drm/exynos/exynos_dp_core.c
	drivers/gpu/drm/exynos/exynos_drm_dpi.c
	drivers/gpu/drm/exynos/exynos_drm_dsi.c
	drivers/gpu/drm/exynos/exynos_drm_vidi.c
	drivers/gpu/drm/exynos/exynos_hdmi.c
	drivers/gpu/drm/gma500/cdv_intel_lvds.c
	drivers/gpu/drm/gma500/oaktrail_lvds.c
	drivers/gpu/drm/gma500/psb_intel_lvds.c
	drivers/gpu/drm/i915/intel_sdvo.c
	drivers/gpu/drm/nouveau/nouveau_connector.c
	drivers/gpu/drm/radeon/radeon_connectors.c
	drivers/staging/imx-drm/imx-drm-core.c