drm: Convert connector_helper_funcs->atomic_check to accept drm_atomic_state

Everyone who implements connector_helper_funcs->atomic_check reaches
into the connector state to get the atomic state. Instead of continuing
this pattern, change the callback signature to just give atomic state
and let the driver determine what it does and does not need from it.

Eventually all atomic functions should do this, but that's just too much
busy work for me.

Changes in v3:
- Added to the set
Changes in v4:
- None
Changes in v5:
- intel_digital_connector_atomic_check declaration moved to i915_atomic.h

Link to v3: https://patchwork.freedesktop.org/patch/msgid/20190502194956.218441-5-sean@poorly.run
Link to v4: https://patchwork.freedesktop.org/patch/msgid/20190508160920.144739-5-sean@poorly.run



Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Cc: Eric Anholt <eric@anholt.net>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> [for rcar lvds]
Acked-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190611160844.257498-5-sean@poorly.run