Even though we only support atomic plane updates at the moment, we still
need to add an .atomic_get_property() entrypoint for connectors before
we allow the driver to flip on the DRIVER_ATOMIC bit.  As soon as that
bit gets set, the DRM core will start adding atomic connector properties
(in addition to the plane properties we care about at the moment), so we
need to be able to handle the new way the DRM core will interact with
us.

For simplicity, we just lookup driver-specific connector properties in
the usual shadow array maintained by the core.  Once we get real atomic
modeset support for crtc's and planes, this code should be re-written to
pull the data out of crtc/connector state structures.

v2: Fix intel_dvo and intel_dsi that I missed on the first pass (Ander)
Signed-off-by: NMatt Roper <matthew.d.roper@intel.com>
Reviewed-by: NAnder Conselvan de Oliveira <conselvan2@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Add the top-level atomic entrypoints for check/commit.  These won't get
called yet; we still need to either enable the atomic ioctl or switch to
using the non-transitional atomic helpers for legacy operations.

v2:
 - Use plane->pipe rather than plane->possible_crtcs while ensuring that
   only a single CRTC is in use.  Either way will work fine since i915
   drm_plane's are always tied to a single CRTC, but plane->pipe is
   slightly more intuitive. (Ander)
 - Simplify crtc/connector checking logic. (Ander)
Signed-off-by: NMatt Roper <matthew.d.roper@intel.com>
Reviewed-by: NAnder Conselvan de Oliveira <conselvan2@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>