drm: Nuke drm_atomic_helper_plane_set_property

It's dead code, the core handles all this directly now. This also
allows us to unexport drm_atomic_plane_set_property.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Brian Starkey <brian.starkey@arm.com>
Cc: Mali DP Maintainers <malidp@foss.arm.com>
Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Inki Dae <inki.dae@samsung.com>
Cc: Joonyoung Shim <jy0922.shim@samsung.com>
Cc: Seung-Woo Kim <sw0312.kim@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Kukjin Kim <kgene@kernel.org>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Cc: Vincent Abriou <vincent.abriou@st.com>
Cc: Yannick Fertre <yannick.fertre@st.com>
Cc: Philippe Cornu <philippe.cornu@st.com>
Cc: Jyri Sarha <jsarha@ti.com>
Cc: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
Cc: Rongrong Zou <zourongrong@gmail.com>
Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Eric Engestrom <eric@engestrom.ch>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Archit Taneja <architt@codeaurora.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-samsung-soc@vger.kernel.org
Cc: intel-gfx@lists.freedesktop.org
Cc: nouveau@lists.freedesktop.org
Cc: linux-renesas-soc@vger.kernel.org
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Maxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170725080122.20548-6-daniel.vetter@ffwll.ch
Reviewed-by: Archit Taneja <architt@codeaurora.org>
Acked-by: Philippe Cornu <philippe.cornu@st.com>
Tested-by: Philippe Cornu <philippe.cornu@st.com>
Acked-by: Liviu Dudau <Liviu.Dudau@arm.com>
Acked-by: Vincent Abriou <vincent.abriou@st.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>